10-Q

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

 _______________________________________________________________________

Form 10-Q

_______________________________________________________________________

(Mark One)

ý QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the quarterly period ended September 30, 2018

OR

o TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the transition period from              to             

Commission File Number: 001-35186

_______________________________________________________________________

SPIRIT AIRLINES, INC.

(Exact name of registrant as specified in its charter)

_______________________________________________________________________

Delaware	38-1747023
(State or other jurisdiction of incorporation or organization)	(I.R.S. Employer Identification No.)
2800 Executive Way Miramar, Florida	33025
(Address of principal executive offices)	(Zip Code)

(954) 447-7920

(Registrant’s telephone number, including area code) 

_______________________________________________________________________

Indicate by check mark whether the registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    Yes  ý  No  o

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§ 232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).    Yes  ý    No  o

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “small reporting company” and "emerging growth company" in Rule 12b-2 of the Exchange Act. (Check one):

Large accelerated filer	ý	Accelerated filer	o
Non-accelerated filer	o	Smaller reporting company	o
(Do not check if a smaller reporting company)		Emerging growth company	o

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act.     o

Indicate by check mark whether the registrant is a shell company (as defined by Rule 12b-2 of the Exchange Act).    Yes  o    No  ý

Indicate the number of shares outstanding of each of the registrant’s classes of common stock as of the close of business on October 18, 2018:

Class	Number of Shares
Common Stock, $0.0001 par value	68,264,513

Table of Contents

INDEX

			Page No.
Part I. Financial Information
	Item 1.	Condensed Financial Statements (unaudited)	1
		Condensed Statements of Operations - Three and Nine Months Ended September 30, 2018 and 2017	1
		Condensed Statements of Comprehensive Income - Three and Nine Months Ended September 30, 2018 and 2017	2
		Condensed Balance Sheets – September 30, 2018 and December 31, 2017	3
		Condensed Statements of Cash Flows – Nine Months Ended September 30, 2018 and 2017	4
		Notes to Condensed Financial Statements	5
	Item 2.	Management’s Discussion and Analysis of Financial Condition and Results of Operations	28
		Glossary of Airline Terms	43
	Item 3.	Quantitative and Qualitative Disclosures About Market Risk	45
	Item 4.	Controls and Procedures	46
Part II. Other Information
	Item 1.	Legal Proceedings	47
	Item 1A.	Risk Factors	48
	Item 2.	Unregistered Sales of Equity Securities and Use of Proceeds	49
	Item 3.	Defaults Upon Senior Securities	49
	Item 4.	Mine Safety Disclosures	49
	Item 5.	Other Information	49
	Item 6.	Exhibits	50
Signature			51

PART I. Financial Information

ITEM 1. UNAUDITED CONDENSED FINANCIAL STATEMENTS

Spirit Airlines, Inc.

Condensed Statements of Operations

(unaudited, in thousands, except per share amounts)

	Three Months Ended September 30,						Nine Months Ended September 30,
	2018			2017			2018			2017
Operating revenues:
Passenger	$	887,956		$	669,072		$	2,413,447		$	1,922,239
Other	16,374			18,155			46,792			55,130
Total operating revenues	904,330			687,227			2,460,239			1,977,369
Operating expenses:
Aircraft fuel	258,818			158,300			709,644			440,376
Salaries, wages and benefits	185,043			134,114			527,895			391,144
Aircraft rent	42,682			53,396			134,618			163,032
Landing fees and other rents	54,542			48,498			162,774			134,538
Depreciation and amortization	43,773			36,840			128,764			103,680
Maintenance, materials and repairs	37,778			26,176			99,141			81,473
Distribution	37,868			29,695			103,496			85,302
Special charges (credits)	(686		)	7,853			88,656			12,629
Loss on disposal of assets	1,069			516			6,561			3,114
Other operating	98,318			87,965			283,841			268,553
Total operating expenses	759,205			583,353			2,245,390			1,683,841
Operating income	145,125			103,874			214,849			293,528
Other (income) expense:
Interest expense	21,925			15,018			60,272			41,237
Capitalized interest	(2,657		)	(3,203		)	(7,205		)	(10,125		)
Interest income	(4,776		)	(2,605		)	(13,272		)	(5,746		)
Other expense	302			114			623			221
Special charges, non-operating	1,744			—			90,357			—
Total other (income) expense	16,538			9,324			130,775			25,587
Income before income taxes	128,587			94,550			84,074			267,941
Provision for income taxes	31,107			34,506			20,262			99,395
Net income	$	97,480		$	60,044		$	63,812		$	168,546
Basic earnings per share	$	1.43		$	0.87		$	0.94		$	2.43
Diluted earnings per share	$	1.42		$	0.86		$	0.93		$	2.42

The accompanying Notes are an integral part of these Condensed Financial Statements.

1

Spirit Airlines, Inc.

Condensed Statements of Comprehensive Income

(unaudited, in thousands)

	Three Months Ended September 30,					Nine Months Ended September 30,
	2018			2017		2018		2017
Net income	$	97,480		$	60,044	$	63,812	$	168,546
Unrealized gain (loss) on short-term investment securities, net of deferred taxes of $(5), $7, $21 and ($6)	(7		)	13		70		(11		)
Interest rate derivative loss reclassified into earnings, net of taxes of $27, $31, $66 and $92	52			53		172		160
Other comprehensive income	$	45		$	66	$	242	$	149
Comprehensive income	$	97,525		$	60,110	$	64,054	$	168,695

The accompanying Notes are an integral part of these Condensed Financial Statements.

2

Spirit Airlines, Inc.

Condensed Balance Sheets

(unaudited, in thousands)

	September 30, 2018			December 31, 2017
Assets
Current assets:
Cash and cash equivalents	$	773,710		$	800,849
Short-term investment securities	102,201			100,937
Accounts receivable, net	63,526			49,323
Aircraft maintenance deposits, net	104,472			175,615
Income tax receivable	78,506			69,844
Prepaid expenses and other current assets	83,692			85,542
Total current assets	1,206,107			1,282,110
Property and equipment:
Flight equipment	3,023,898			2,291,110
Ground property and equipment	178,339			155,166
Less accumulated depreciation	(296,157		)	(207,808		)
	2,906,080			2,238,468
Deposits on flight equipment purchase contracts	253,825			253,687
Long-term aircraft maintenance deposits	144,642			150,617
Deferred heavy maintenance, net	191,632			99,915
Other long-term assets	79,445			121,003
Total assets	$	4,781,731		$	4,145,800
Liabilities and shareholders’ equity
Current liabilities:
Accounts payable	$	63,190		$	22,822
Air traffic liability	323,627			263,711
Current maturities of long-term debt and capital leases	150,862			115,430
Other current liabilities	287,142			262,370
Total current liabilities	824,821			664,333
Long-term debt and capital leases, less current maturities	1,770,904			1,387,498
Deferred income taxes	332,119			308,814
Deferred gains and other long-term liabilities	20,105			22,581
Shareholders’ equity:
Common stock	7			7
Additional paid-in-capital	368,451			360,153
Treasury stock, at cost	(66,999		)	(65,854		)
Retained earnings	1,533,545			1,469,732
Accumulated other comprehensive income (loss)	(1,222		)	(1,464		)
Total shareholders’ equity	1,833,782			1,762,574
Total liabilities and shareholders’ equity	$	4,781,731		$	4,145,800

The accompanying Notes are an integral part of these Condensed Financial Statements.

3

Spirit Airlines, Inc.

Condensed Statements of Cash Flows

(unaudited, in thousands) 

	Nine Months Ended September 30,
	2018			2017
Operating activities:
Net income	$	63,812		$	168,546
Adjustments to reconcile net income to net cash provided by operations:
Losses reclassified from other comprehensive income	238			252
Stock-based compensation	8,293			6,723
Allowance for doubtful accounts (recoveries)	(12		)	(53		)
Amortization of deferred gains and losses and debt issuance costs	6,508			6,415
Depreciation and amortization	128,764			103,680
Deferred income tax expense	21,243			97,833
Loss on disposal of assets	6,561			3,114
Lease termination costs	—			12,629
Special charges, non-operating	90,357			—
Changes in operating assets and liabilities:
Accounts receivable	(14,191		)	(5,046		)
Aircraft maintenance deposits, net	10,543			(28,422		)
Prepaid income taxes	—			(160		)
Long-term deposits and other assets	(5,760		)	(69,307		)
Deferred heavy maintenance	(121,643		)	(12,032		)
Income tax receivable	(8,662		)	—
Accounts payable	38,771			13,829
Air traffic liability	59,916			73,639
Other liabilities	23,896			15,345
Other	(136		)	339
Net cash provided by operating activities	308,498			387,324
Investing activities:
Purchase of available-for-sale investment securities	(100,228		)	(96,851		)
Proceeds from the maturity of available-for-sale investment securities	99,134			95,881
Proceeds from sale of property and equipment	9,500			—
Pre-delivery deposits for flight equipment, net of refunds	(132,297		)	(121,702		)
Capitalized interest	(6,116		)	(8,054		)
Purchase of property and equipment	(420,586		)	(428,913		)
Net cash used in investing activities	(550,593		)	(559,639		)
Financing activities:
Proceeds from issuance of long-term debt	518,171			405,827
Proceeds from stock options exercised	5			45
Payments on debt obligations	(93,225		)	(63,352		)
Payments on capital lease obligations	(205,566		)	(291		)
Repurchase of common stock	(1,145		)	(1,238		)
Debt issuance costs	(3,284		)	(5,896		)
Net cash provided by financing activities	214,956			335,095
Net (decrease) increase in cash and cash equivalents	(27,139		)	162,780
Cash and cash equivalents at beginning of period	800,849			700,900
Cash and cash equivalents at end of period	$	773,710		$	863,680
Supplemental disclosures
Cash payments for:
Interest, net of capitalized interest	$	35,977		$	22,541
Income taxes paid, net of refunds	$	3,366		$	4,352
Non-cash transactions:
Capital expenditures funded by capital lease borrowings	$	(315	)	$	(1,370	)

The accompanying Notes are an integral part of these Condensed Financial Statements.

4

Notes to Condensed Financial Statements

(unaudited)

1. Basis of Presentation

The accompanying unaudited condensed financial statements include the accounts of Spirit Airlines, Inc. ("the Company"). These unaudited condensed financial statements reflect all normal recurring adjustments which management believes are necessary to fairly present the financial position, results of operations and cash flows of the Company for the respective periods presented. Certain information and footnote disclosures normally included in the annual financial statements prepared in accordance with U.S. generally accepted accounting principles ("GAAP") have been condensed or omitted pursuant to the rules and regulations of the Securities and Exchange Commission for Form 10-Q. These unaudited interim condensed financial statements should be read in conjunction with the audited financial statements of the Company and notes thereto included in the Company's Annual Report on Form 10-K for the year ended December 31, 2017 filed with the Securities and Exchange Commission on February 13, 2018.

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect both the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from these estimates.

The interim results reflected in the unaudited condensed financial statements are not necessarily indicative of the results that may be expected for other interim periods or for the full year.

Certain prior period amounts have been reclassified to conform to the current year's presentation and the adoption of Accounting Standards Update ("ASU") No. 2014-09, ("ASU 2014-09") "Revenue from Contracts with Customers".

2. Recent Accounting Developments

Recently Adopted Accounting Pronouncements

Revenue from Contracts with Customers

In May 2014, the Financial Accounting Standards Board ("the FASB") issued Accounting Standards Update ("ASU") No. 2014-09, ("ASU 2014-09") "Revenue from Contracts with Customers." The objective of ASU 2014-09 is to establish a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers. The Company adopted this guidance on January 1, 2018 utilizing the full retrospective method of adoption allowed by the standard, in order to provide for comparative results in all periods presented. The most significant impact of this ASU is the elimination of the incremental cost method for frequent flier program accounting, which requires the Company to re-value and record a liability associated with customer flight miles earned as part of the Company’s frequent flier program with a relative fair value approach. The classification and timing of recognition of certain ancillary fees is also impacted by the adoption of ASU 2014-09. While the adoption did not have a significant impact on earnings, the classification of certain revenues, such as bags, seats and other travel-related fees are now deemed part of the single performance obligation of providing passenger transportation. Refer to Note 3, Revenue Recognition for information regarding the Company's adoption of ASU 2014-09 and to Note 4, Revenue Disaggregation for the presentation of passenger revenues disaggregated by fare and non-fare.

Financial Instruments

In January 2016, the FASB issued ASU 2016-01, “Financial Instruments – Overall (Subtopic 825-10).” ASU 2016-01 makes several modifications to Subtopic 825-10 including the elimination of the available-for-sale classification of equity investments, and requires equity investments with readily determinable fair values to be measured at fair value with changes in fair value recognized in net income. ASU 2016-01 is effective for the Company for interim and annual periods beginning January 1, 2018. The Company adopted this guidance on January 1, 2018 with no material impact on the financial statements.

Statement of Cash Flows

In August 2016, the FASB issued ASU No. 2016-15, "Statement of Cash Flows." The standard is intended to reduce diversity in practice in how certain transactions are classified in the statement of cash flows. This standard is effective for the

5

Notes to Condensed Financial Statements—(Continued)

Company for fiscal years, and interim periods within those years, beginning January 1, 2018. The Company adopted this guidance on January 1, 2018 with no material impact on the financial statements.

Recently Issued Accounting Pronouncements Not Yet Adopted

Leases

In February 2016, the FASB issued ASU No. 2016-02, "Leases (Topic 842)." This standard will require all lessees to recognize a right-of-use asset and a lease liability, initially measured at the present value of the lease payments, for all leases with a term greater than 12 months. The standard is effective for the Company effective January 1, 2019. Early adoption is permitted. However, the Company does not plan to early adopt. The Company has established a cross functional project plan and is in the process of testing items necessary to account for the new standard. The Company expects this standard to have a significant impact on its condensed balance sheets due to the recognition of right-of-use assets and lease liabilities for leases. The Company does not expect the adoption to have a significant impact on its lease classification, a material impact on its condensed statement of operations, or a notable impact on its liquidity. Additionally, the Company does not expect the standard to have a material impact on the Company’s debt-covenant compliance under its current agreements. Refer to Note 10, Commitments and Contingencies for information regarding the Company's undiscounted future lease payments and the timing of those payments. 

In July 2018, the FASB issued additional guidance on the accounting for leases. The guidance provides companies with another transition method that allows entities to recognize a cumulative-effect adjustment to the opening balance of retained earnings as of the date of adoption. Under this method, previously presented years’ financial positions and results would not be adjusted. The new guidance also provides lessors with a practical expedient, by class of underlying asset, to not separate non-lease components from the associated lease component if (1) the non-lease components would otherwise be accounted for under the new revenue recognition standard, (2) both the timing and pattern of transfer are the same for the non-lease components and associated lease component, and (3) if accounted for separately, the lease component would be classified as an operating lease. The Company is assessing the use of practical expedients in its accounting for leases.

Accounting for Credit Losses

In June 2016, the FASB issued ASU No. 2016-13, "Financial Instruments - Credit Losses." The standard requires the use of an "expected loss" model on certain types of financial instruments. The standard also amends the impairment model for available-for-sale securities and requires estimated credit losses to be recorded as allowances rather than as reductions to the amortized cost of the securities. This standard is effective for the Company for fiscal years, and interim periods within those years, beginning January 1, 2020, with early adoption permitted. The Company is evaluating the new guidance, but does not expect it to have a material impact on its financial statements.

Income Taxes

In March 2018, the FASB issued ASU 2018-05, Income Taxes ("Topic 740") - Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 118. The standard amends Accounting Standards Codification 740, Income Taxes ("ASC 740") to provide guidance on accounting for the tax effects of the Tax Cuts and Jobs Act (the "Tax Act") pursuant to Staff Accounting Bulletin No. 118. The provisional income tax amounts recorded may be affected as the Company gains a more thorough understanding of the tax law, including those related to the deductibility of acquired assets, state tax treatment and amounts related to employee compensation. The provisional accounting impacts for the Company may change in future reporting periods until the accounting is finalized, which will occur no later than the fourth quarter of 2018. The Company does not expect material changes to the financial statements in the fourth quarter of 2018 as a result of finalizing the accounting for the Tax Act.

3. Revenue Recognition

Passenger revenues

Fare revenues. Tickets sold are initially deferred as “air traffic liability.” Passenger fare revenues are recognized at time of departure when transportation is provided. All tickets sold by the Company are nonrefundable. An unused ticket expires at the date of scheduled travel and is recognized as revenue at the date of scheduled travel. Passenger revenues reported prior to

6

Notes to Condensed Financial Statements—(Continued)

the adoption of ASU 2014-09 are now reported as fare revenues within passenger revenues in the Company's disaggregated revenue table within Note 4, Revenue Disaggregation.

As of December 31, 2017 and 2016, the Company had air traffic liability ("ATL") balances of  $263.7 million and $220.2 million, respectively. As of September 30, 2018, all of the ATL balance as of December 31, 2017 has been recognized.

Non-fare revenues.The adoption of ASU 2014-09 impacted the classification of certain ancillary items such as bags, seats and other travel-related fees, since they are deemed part of the single performance obligation of providing passenger transportation. These ancillary items are now recognized in non-fare revenues within passenger revenues in the Company's disaggregated revenue table within Note 4, Revenue Disaggregation.

Changes and cancellations. Customers may elect to change or cancel their itinerary prior to the date of departure. For changes, a service charge is recognized at time of departure of newly scheduled travel and is deducted from the face value of the original purchase price of the ticket, and the original ticket becomes invalid. For cancellations, a service charge is assessed and the amount remaining after deducting the service charge is called a credit shell which generally expires 60 days from the date the credit shell is created and can be used towards the purchase of a new ticket and the Company’s other service offerings. Both the service charge and credit shell amounts are recorded as deferred revenue and amounts expected to expire unused are estimated based on historical experience. Estimating the amount of credits that will go unused involves some level of subjectivity and judgment. However, given the relatively short period of time to expiration, this does not have a significant impact on the Company's financial statements.

Other revenues

Other revenues primarily consist of the marketing component of the sale of frequent flyer miles to the Company's credit card partner and commissions revenue from the sale of various items such as hotels and rental cars.

Frequent Flyer Program

The Company's frequent flyer program generates customer loyalty by rewarding customers with mileage credits to travel on Spirit. When traveling, customers earn redeemable mileage credits for each mile flown on Spirit. Customers can also earn mileage credits through participating companies such as the co-branded Spirit credit card. Mileage credits are redeemable by customers in future periods for air travel on Spirit.

To reflect the mileage credits earned, the program includes two types of transactions that are considered revenue arrangements with multiple performance obligations: (1) mileage credits earned with travel and (2) mileage credits sold to co-branded credit card partner.

The adoption of ASU 2014-09 eliminated the incremental cost method for frequent flier program accounting, which required the Company to re-value and record a liability associated with customer flight miles earned with travel as part of the Company’s frequent flier program with a relative fair value. Upon adoption of ASU 2014-09 on January 1, 2018, the Company recorded an increase to its air traffic liability of $12.4 million.

Passenger ticket sales earning mileage credits. Passenger ticket sales earning mileage credits provide customers with (1) mileage credits earned and (2) air transportation. The Company values each performance obligation on a standalone basis. To value the mileage credits earned, the Company considers the quantitative value a passenger receives by redeeming miles for a ticket rather than paying cash, which is referred to as equivalent ticket value ("ETV").

The Company defers revenue for the mileage credits when earned and recognizes loyalty travel awards in passenger revenue as the miles are redeemed and services are provided. The Company records the air transportation portion of the passenger ticket sales in air traffic liability and recognizes passenger revenue when transportation is provided or if the ticket goes unused.

Sale of mileage credits. Customers may earn mileage credits based on their spending with the Company's co-branded credit card company with which the Company has an agreement to sell mileage credits. The contract to sell mileage credits under this agreement has multiple performance obligations. During the nine months ended September 30, 2018 and 2017, total cash sales from this agreement were $29.6 million and $38.1 million, respectively, which are allocated to travel and other performance obligations, as discussed below.

7

Notes to Condensed Financial Statements—(Continued)

The Company's co-brand credit card agreement provides for joint marketing where cardholders earn mileage credits for making purchases using co-branded cards. During 2015, the Company extended its agreement with the administrator of the FREE SPIRIT affinity credit card program to extend through 2022. The Company accounts for this agreement consistently with the accounting method that allocates the consideration received to the individual products and services delivered. The value is allocated based on the relative selling prices of those products and services, which generally consists of (i) travel miles to be awarded, (ii) licensing of brand and access to member lists and (iii) advertising and marketing efforts. The Company determined the best estimate of the selling prices by considering discounted cash flow analysis using multiple inputs and assumptions, including: (1) the expected number of miles awarded and number of miles redeemed, (2) ETV for the award travel obligation, (3) licensing of brand and access to member lists and (4) advertising and marketing efforts. 

The Company defers the amount for award travel obligation as part of loyalty deferred revenue within air traffic liability on the balance sheet and recognizes loyalty travel awards in passenger revenue as the mileage credits are used for travel. Revenue allocated to the remaining performance obligations, primarily marketing components, is recorded in other revenue over time as miles are delivered.

Mileage breakage. For mileage credits that the Company estimates are not likely to be redeemed ("breakage"), the Company recognizes the associated value proportionally during the period in which the remaining mileage credits are redeemed. Management uses statistical models to estimate breakage based on historical redemption patterns. A change in assumptions as to the period over which mileage credits are expected to be redeemed, the actual redemption activity for mileage credits or the estimated fair value of mileage credits expected to be redeemed could have an impact on revenues in the year in which the change occurs and in future years.

Current activity of frequent flyer program. Mileage credits are combined in one homogeneous pool and are not separately identifiable. As such, revenue is comprised of miles that were part of the frequent flyer deferred revenue balance at the beginning of the period as well as miles that were issued during the period.

The following tables show adjustments made due to the adoption of ASU 2014-09 on the December 31, 2017 and 2016 statements of operations. Previously reported results were derived from audited financial statements included in Company's Annual Report on Form 10-K for the fiscal years ended December 31, 2017 and December 31, 2016, as applicable.

8

Notes to Condensed Financial Statements—(Continued)

	Year Ended December 31, 2017
	(in thousands, except share and per share data)
	As Reported			Topic 606 Adjustment			As Adjusted
Operating revenues:
Passenger	$	1,366,034		$	1,206,853		$	2,572,887
Other	1,281,632			(1,210,967		)	70,665
Total operating revenues	2,647,666			(4,114		)	2,643,552
Operating expenses:
Aircraft fuel	615,581			—			615,581
Salaries, wages and benefits	527,959			—			527,959
Aircraft rent	205,852			—			205,852
Landing fees and other rents	180,655			—			180,655
Depreciation and amortization	140,152			—			140,152
Maintenance, materials and repairs	110,439			—			110,439
Distribution	113,620			(148		)	113,472
Special charges	12,629			—			12,629
Loss on disposal of assets	4,168			—			4,168
Other operating	347,820			—			347,820
Total operating expenses	2,258,875			(148		)	2,258,727
Operating income	388,791			(3,966		)	384,825
Other (income) expense:
Interest expense	57,302			—			57,302
Capitalized interest	(13,793		)	—			(13,793		)
Interest income	(8,736		)	—			(8,736		)
Other expense	366			—			366
Total other (income) expense	35,139			—			35,139
Income before income taxes	353,652			(3,966		)	349,686
Provision (benefit) for income taxes	(66,954		)	1,118			(65,836		)
Net income	$	420,606		$	(5,084	)	$	415,522
Basic earnings per share	$	6.08		$	(0.07	)	$	6.00
Diluted earnings per share	$	6.06		$	(0.07	)	$	5.99

9

Notes to Condensed Financial Statements—(Continued)

	Year Ended December 31, 2016
	(in thousands, except share and per share data)
	As Reported			Topic 606 Adjustment			As Adjusted
Operating revenues:
Passenger	$	1,200,621		$	1,057,180		$	2,257,801
Other	1,121,335			(1,059,115		)	62,220
Total operating revenues	2,321,956			(1,935		)	2,320,021
Operating expenses:
Salaries, wages and benefits	472,471			—			472,471
Aircraft fuel	447,553			—			447,553
Aircraft rent	201,675			—			201,675
Landing fees and other rents	151,679			—			151,679
Depreciation and amortization	101,136			—			101,136
Maintenance, materials and repairs	98,587			—			98,587
Distribution	96,627			268			96,895
Special charges	37,189			—			37,189
Loss on disposal of assets	4,187			—			4,187
Other operating	267,191			—			267,191
Total operating expenses	1,878,295			268			1,878,563
Operating income	443,661			(2,203		)	441,458
Other (income) expense:
Interest expense	41,654			—			41,654
Capitalized interest	(12,705		)	—			(12,705		)
Interest income	(5,276		)	—			(5,276		)
Other expense	528			—			528
Total other (income) expense	24,201			—			24,201
Income before income taxes	419,460			(2,203		)	417,257
Provision (benefit) for income taxes	154,581			(807		)	153,774
Net income	$	264,879		$	(1,396	)	$	263,483
Basic earnings per share	$	3.77		$	(0.02	)	$	3.75
Diluted earnings per share	$	3.76		$	(0.02	)	$	3.74

10

Notes to Condensed Financial Statements—(Continued)

The following table shows adjusted balances after the adoption of ASU 2014-09 on the quarterly statements of operations for each quarter of 2017.

	For the Quarter Ended
	March 31, 2017			June 30, 2017			September 30, 2017			December 31, 2017
	(in thousands, except share and per share data)
Operating revenues:
Passenger	$	572,287		$	680,880		$	669,072		$	650,647
Other	17,670			19,305			18,155			15,535
Total operating revenues	589,957			700,185			687,227			666,182
Operating expenses:
Aircraft fuel	139,782			142,294			158,300			175,205
Salaries, wages and benefits	127,138			129,892			134,114			136,815
Aircraft rent	57,070			52,566			53,396			42,820
Landing fees and other rents	40,448			45,592			48,498			46,117
Depreciation and amortization	31,509			35,331			36,840			36,472
Maintenance, materials and repairs	26,312			28,985			26,176			28,966
Distribution	25,772			29,835			29,695			28,170
Special charges	4,776			—			7,853			—
Loss on disposal of assets	1,105			1,493			516			1,054
Other operating	77,703			102,885			87,965			79,267
Total operating expenses	531,615			568,873			583,353			574,886
Operating income	58,342			131,312			103,874			91,296
Other (income) expense:
Interest expense	12,473			13,746			15,018			16,065
Capitalized interest	(3,580		)	(3,342		)	(3,203		)	(3,668		)
Interest income	(1,313		)	(1,828		)	(2,605		)	(2,990		)
Other expense	3			104			114			145
Total other (income) expense	7,583			8,680			9,324			9,552
Income before income taxes	50,759			122,632			94,550			81,744
Provision (benefit) for income taxes	19,498			45,391			34,506			(165,231		)
Net income	$	31,261		$	77,241		$	60,044		$	246,975
Basic earnings per share	$	0.45		$	1.11		$	0.87		$	3.59
Diluted earnings per share	$	0.45		$	1.11		$	0.86		$	3.58

11

Notes to Condensed Financial Statements—(Continued)

The following table shows quarterly adjustments made due to the adoption of ASU 2014-09 on the statements of operations for 2017.

				Adjustments for the Quarter Ended
	Full Year 2017 As Reported			March 31, 2017			June 30, 2017			September 30, 2017			December 31, 2017			Full Year 2017 Adjusted
	(in thousands, except share and per share data)
Operating revenues:
Passenger	$	1,366,034		$	272,525		$	308,959		$	312,865		$	312,504		$	2,572,887
Other	1,281,632			(274,314		)	(310,455		)	(312,869		)	(313,329		)	70,665
Total operating revenues	2,647,666			(1,789		)	(1,496		)	(4		)	(825		)	2,643,552
Operating expenses:
Aircraft fuel	615,581			—			—			—			—			615,581
Salaries, wages and benefits	527,959			—			—			—			—			527,959
Aircraft rent	205,852			—			—			—			—			205,852
Landing fees and other rents	180,655			—			—			—			—			180,655
Depreciation and amortization	140,152			—			—			—			—			140,152
Maintenance, materials and repairs	110,439			—			—			—			—			110,439
Distribution	113,620			(726		)	(73		)	226			425			113,472
Special charges	12,629			—			—			—			—			12,629
Loss on disposal of assets	4,168			—			—			—			—			4,168
Other operating	347,820			—			—			—			—			347,820
Total operating expenses	2,258,875			(726		)	(73		)	226			425			2,258,727
Operating income	388,791			(1,063		)	(1,423		)	(230		)	(1,250		)	384,825
Other (income) expense:
Interest expense	57,302			—			—			—			—			57,302
Capitalized interest	(13,793		)	—			—			—			—			(13,793		)
Interest income	(8,736		)	—			—			—			—			(8,736		)
Other expense	366			—			—			—			—			366
Total other (income) expense	35,139			—			—			—			—			35,139
Income before income taxes	353,652			(1,063		)	(1,423		)	(230		)	(1,250		)	349,686
Provision (benefit) for income taxes	(66,954		)	(389		)	(522		)	(84		)	2,113			(65,836		)
Net income	$	420,606		$	(674	)	$	(901	)	$	(146	)	$	(3,363	)	$	415,522
Basic earnings per share	$	6.08		$	(0.01	)	$	(0.01	)	$	—		$	(0.05	)	$	6.00
Diluted earnings per share	$	6.06		$	(0.01	)	$	(0.01	)	$	—		$	(0.05	)	$	5.99

12

Notes to Condensed Financial Statements—(Continued)

The following tables show adjustments made due to the adoption of ASU 2014-09 on the December 31, 2017 and 2016 balance sheets. Previously reported results were derived from audited financial statements included in Company's Annual Report on Form 10-K for the fiscal years ended December 31, 2017 and December 31, 2016, as applicable.

	December 31, 2017
	(in thousands)
	As Reported			Topic 606 Adjustment			As Adjusted
Assets
Current assets:
Cash and cash equivalents	$	800,849		$	—		$	800,849
Short-term investment securities	100,937			—			100,937
Accounts receivable, net	49,323			—			49,323
Aircraft maintenance deposits, net	175,615			—			175,615
Income tax receivable	69,844			—			69,844
Prepaid expenses and other current assets	83,692			1,850			85,542
Total current assets	1,280,260			1,850			1,282,110
Property and equipment:
Flight equipment	2,291,110			—			2,291,110
Ground property and equipment	155,166			—			155,166
Less accumulated depreciation	(207,808		)	—			(207,808		)
	2,238,468			—			2,238,468
Deposits on flight equipment purchase contracts	253,687			—			253,687
Long-term aircraft maintenance deposits	150,617			—			150,617
Deferred heavy maintenance, net	99,915			—			99,915
Other long-term assets	121,003			—			121,003
Total assets	$	4,143,950		$	1,850		$	4,145,800
Liabilities and shareholders’ equity
Current liabilities:
Accounts payable	$	22,822		$	—		$	22,822
Air traffic liability	246,404			17,307			263,711
Current maturities of long-term debt	115,430			—			115,430
Other current liabilities	262,370			—			262,370
Total current liabilities	647,026			17,307			664,333
Long-term debt, less current maturities	1,387,498			—			1,387,498
Deferred income taxes	313,140			(4,326		)	308,814
Deferred gains and other long-term liabilities	19,205			3,376			22,581
Shareholders’ equity:
Common stock: Common stock, $0.0001 par value, 240,000,000 shares authorized at December 31, 2017; 69,770,795 issued and 68,196,964 outstanding as of December 31, 2017	7			—			7
Additional paid-in-capital	360,153			—			360,153
Treasury stock, at cost: 1,573,831 shares as of December 31, 2017	(65,854		)	—			(65,854		)
Retained earnings	1,484,239			(14,507		)	1,469,732
Accumulated other comprehensive income (loss)	(1,464		)	—			(1,464		)
Total shareholders’ equity	1,777,081			(14,507		)	1,762,574
Total liabilities and shareholders’ equity	$	4,143,950		$	1,850		$	4,145,800

13

Notes to Condensed Financial Statements—(Continued)

	December 31, 2016
	(in thousands)
	As Reported			Topic 606 Adjustment			As Adjusted
Assets
Current assets:
Cash and cash equivalents	$	700,900		$	—		$	700,900
Short-term investment securities	100,155			—			100,155
Accounts receivable, net	41,136			—			41,136
Aircraft maintenance deposits, net	87,035			—			87,035
Income tax receivable	—			—			—
Prepaid expenses and other current assets	46,619			1,702			48,321
Total current assets	975,845			1,702			977,547
Property and equipment:
Flight equipment	1,461,525			—			1,461,525
Ground property and equipment	126,206			—			126,206
Less accumulated depreciation	(122,509		)	—			(122,509		)
	1,465,222			—			1,465,222
Deposits on flight equipment purchase contracts	325,688			—			325,688
Long-term aircraft maintenance deposits	199,415			—			199,415
Deferred heavy maintenance, net	75,534			—			75,534
Other long-term assets	110,223			—			110,223
Total assets	$	3,151,927		$	1,702		$	3,153,629
Liabilities and shareholders’ equity
Current liabilities:
Accounts payable	$	15,193		$	—		$	15,193
Air traffic liability	206,392			13,792			220,184
Current maturities of long-term debt	84,354			—			84,354
Other current liabilities	226,011			—			226,011
Total current liabilities	531,950			13,792			545,742
Long-term debt, less current maturities	897,359			—			897,359
Deferred income taxes	308,143			(5,443		)	302,700
Deferred gains and other long-term liabilities	19,868			2,776			22,644
Shareholders’ equity:
Common stock: Common stock, $0.0001 par value, 240,000,000 shares authorized at December 31, 2016; 73,549,872 issued and 69,326,202 outstanding as of December 31, 2016	7			—			7
Additional paid-in-capital	551,004			—			551,004
Treasury stock, at cost: 4,223,670 shares as of December 31, 2016	(218,692		)	—			(218,692		)
Retained earnings	1,063,633			(9,423		)	1,054,210
Accumulated other comprehensive income (loss)	(1,345		)	—			(1,345		)
Total shareholders’ equity	1,394,607			(9,423		)	1,385,184
Total liabilities and shareholders’ equity	$	3,151,927		$	1,702		$	3,153,629

14

Notes to Condensed Financial Statements—(Continued)

4. Revenue Disaggregation

Operating revenues is comprised of passenger revenues, which includes fare and non-fare revenues, and other revenues. The following table shows disaggregated operating revenues for each quarter of 2018 and 2017.

	For the Quarter Ended
	September 30, 2018		June 30, 2018		March 31, 2018		December 31, 2017		September 30, 2017		June 30, 2017		March 31, 2017
	(in thousands)
Operating revenues:
Fare	$	476,660	$	439,549	$	342,695	$	337,324	$	355,593	$	371,443	$	299,035
Non-fare	411,296		396,801		346,446		313,323		313,479		309,437		273,252
Total passenger revenues	887,956		836,350		689,141		650,647		669,072		680,880		572,287
Other revenues	16,374		15,421		14,997		15,535		18,155		19,305		17,670
Total operating revenues	$	904,330	$	851,771	$	704,138	$	666,182	$	687,227	$	700,185	$	589,957

The following table shows disaggregated operating revenues for years ended December 31, 2017 and 2016.    

	Year Ended December 31,
	2017							2016
	(in thousands)
	As Reported		Topic 606 Adjustment			As Adjusted		As Reported		Topic 606 Adjustment			As Adjusted
Operating revenues:
Fare	$	1,366,034	$	(2,639	)	$	1,363,395	$	1,200,621	$	(2,514	)	$	1,198,107
Non-fare	—		1,209,492			1,209,492		—		1,059,694			1,059,694
Total passenger revenues	1,366,034		1,206,853			2,572,887		1,200,621		1,057,180			2,257,801
Other revenues	1,281,632		(1,210,967		)	70,665		1,121,335		(1,059,115		)	62,220
Total operating revenues	$	2,647,666	$	(4,114	)	$	2,643,552	$	2,321,956	$	(1,935	)	$	2,320,021

The Company is managed as a single business unit that provides air transportation for passengers. Operating revenues by geographic region as defined by the Department of Transportation ("DOT") area are summarized below:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
	(in millions)
DOT—Domestic	$	819.3	$	636.3	$	2,236.3	$	1,819.2
DOT—Latin America	85.0		50.9		223.9		158.2
Total	$	904.3	$	687.2	$	2,460.2	$	1,977.4

5. Special Charges

Special Charges (Credits), Operating

During the first quarter of 2018, the Company negotiated and amended the collective bargaining agreement with the Air Line Pilots Association, International ("ALPA"), under the guidance of the National Mediation Board ("NMB"). In

15

Notes to Condensed Financial Statements—(Continued)

connection with the amended agreement, the Company incurred a one-time ratification incentive of $80.2 million, including payroll taxes, and an $8.5 million adjustment related to other contractual provisions. As a result, the Company recorded $88.7 million in special charges (credits) within operating expenses in the condensed statement of operations for the nine months ended September 30, 2018. As of September 30, 2018, the Company has paid $76.2 million of the ratification incentive with the remainder expected to be paid during the fourth quarter of 2018.

During the nine months ended September 30, 2017, the Company purchased one engine and one aircraft which were previously financed under operating lease agreements. The purchase price of the 1 engine and 1 aircraft was $8.1 million and $20.0 million, respectively, comprised of a cash payment of $3.8 million and $12.6 million, respectively, and the non-cash application of maintenance reserves and security deposits held by the previous lessor of $4.3 million and $7.4 million, respectively. The Company estimated the fair value of the engine and aircraft to be $3.1 million and $11.9 million, respectively, and has recorded the 1 purchased engine and 1 aircraft at fair value within flight equipment on the condensed balance sheets. The Company determined the valuation of the engine and aircraft based on a third-party appraisal considering the condition of the engine and aircraft (a Level 3 measurement). The Company recognized $4.8 million and $7.9 million as a cost of terminating the lease within special charges (credits) in the condensed statement of operations, respectively, made up of the excess of the purchase price paid over the fair value of the engine and the aircraft, less other non-cash items of $0.2 million and $0.2 million, respectively.

Special Charges, Non-Operating

During the nine months ended September 30, 2018, the Company recorded $90.4 million, in special charges, non-operating within other (income) expense in the statement of operations. During the first quarter of 2018, the Company entered into an aircraft purchase agreement for the purchase of 14 A319 aircraft previously operated under operating leases by the Company. The aggregate gross purchase price for the 14 aircraft was $285.0 million, and the price for each aircraft at the time of the sale was comprised of a cash payment net of the amount of maintenance reserves and security deposits for such aircraft held by the applicable lessor pursuant to the lease for such aircraft. The contract was deemed a lease modification which resulted in a change of classification from operating leases to capital leases for the 14 aircraft. During the first quarter of 2018, the capital lease assets were recorded at the lower of cost or fair value of the aircraft within flight equipment on the condensed balance sheets. During the second quarter of 2018, the purchase of the 14 aircraft was completed and the obligation was accreted up to the net cash payment price with interest charges recognized in special charges, non-operating in the statement of operations. The Company determined the valuation of the aircraft based on third-party appraisals considering the condition of the aircraft (a Level 3 measurement). 

6. Earnings per Share

The following table sets forth the computation of basic and diluted earnings per common share:

 

	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
	(in thousands, except per share amounts)
Numerator
Net income	$	97,480	$	60,044	$	63,812	$	168,546
Denominator
Weighted-average shares outstanding, basic	68,254		69,370		68,243		69,363
Effect of dilutive stock awards	249		88		103		174
Adjusted weighted-average shares outstanding, diluted	68,503		69,458		68,346		69,537
Net income per share
Basic earnings per common share	$	1.43	$	0.87	$	0.94	$	2.43
Diluted earnings per common share	$	1.42	$	0.86	$	0.93	$	2.42
Anti-dilutive weighted-average shares	5		124		192		76

16

Notes to Condensed Financial Statements—(Continued)

7. Short-term Investment Securities

The Company's short-term investment securities are classified as available-for-sale and consist of U.S. Treasury and U.S. government agency securities with contractual maturities of 12 months or less. These securities are stated at fair value within current assets on the Company's condensed balance sheets. Realized gains and losses on sales of investments, if any, are reflected in non-operating income (expense) in the condensed statements of operations.

As of September 30, 2018 and December 31, 2017, the Company had $102.2 million and $100.9 million in short-term available-for-sale investment securities, respectively. During the nine months ended September 30, 2018, these investments earned interest income at a weighted-average fixed rate of approximately 1.5%. For the three and nine months ended September 30, 2018, an unrealized loss of $7 thousand and an unrealized gain of $70 thousand, net of deferred taxes of $5 thousand and $21 thousand, respectively, was recorded within accumulated other comprehensive income ("AOCI") related to these investment securities. For the three and nine months ended September 30, 2017, an unrealized gain of $13 thousand and an unrealized loss of $11 thousand, net of deferred taxes of $7 thousand and $6 thousand, respectively, was recorded within AOCI related to these investment securities. The Company has not recognized any realized gains or losses related to these securities as the Company has not transacted any sale of these securities. As of September 30, 2018 and December 31, 2017, $34 thousand and $105 thousand, net of tax, respectively, remained in AOCI, related to these instruments.

8. Accrued Liabilities

Other current liabilities as of September 30, 2018 and December 31, 2017 consist of the following:

	September 30, 2018		December 31, 2017
	(in thousands)
Salaries and wages	$	81,278	$	54,338
Federal excise and other passenger taxes and fees payable	55,743		42,036
Airport obligations	47,476		56,299
Aircraft maintenance	26,438		33,033
Fuel	21,637		25,171
Interest payable	18,965		11,384
Aircraft and facility lease obligations	12,236		16,992
Other	23,369		23,117
Other current liabilities	$	287,142	$	262,370

9. Financial Instruments and Risk Management

As part of the Company’s risk management program, the Company from time to time uses a variety of financial instruments to reduce its exposure to fluctuations in the price of jet fuel and interest rates. The Company does not hold or issue derivative financial instruments for trading purposes.

The Company is exposed to credit losses in the event of nonperformance by counterparties to these financial instruments. The Company periodically reviews and seeks to mitigate exposure to the financial deterioration and nonperformance of any counterparty by monitoring the absolute exposure levels, each counterparty's credit ratings and the historical performance of the counterparties relating to hedge transactions. The credit exposure related to these financial instruments is limited to the fair value of contracts in a net receivable position at the reporting date. The Company also maintains security agreements that require the Company to post collateral if the value of selected instruments falls below specified mark-to-market thresholds. The Company records financial derivative instruments at fair value, which includes an evaluation of each counterparty's credit risk. As of September 30, 2018, the Company did not hold any derivatives with requirements to post collateral.

Fuel Derivative Instruments

From time to time, the Company may enter into fuel derivative contracts in order to mitigate the risk of future volatility in fuel prices. The Company's fuel derivative contracts, if any, generally consist of United States Gulf Coast jet fuel swaps ("jet fuel swaps") and United States Gulf Coast jet fuel options ("jet fuel options"). Both jet fuel swaps and jet fuel options are used at times to protect the refining price risk between the price of crude oil and the price of refined jet fuel, and to manage the risk of increasing fuel prices. Fair value of the instruments is determined using standard option valuation models.

17

Notes to Condensed Financial Statements—(Continued)

The Company accounts for any fuel derivative contracts at fair value and recognizes them in the balance sheet in prepaid expenses and other current assets or other current liabilities. The Company did not enter into any fuel derivative instruments during the nine months ended September 30, 2018 and 2017 and did not have any outstanding fuel derivatives as of September 30, 2018 and December 31, 2017. Historically, the Company has not elected hedge accounting on any fuel derivative instruments entered into and, as a result, changes in the fair value of fuel derivative contracts, if any, were recorded in aircraft fuel expense.

Interest Rate Swaps

From time to time, the Company may enter into interest rate swaps to fix the benchmark interest rate component of interest payments or for other reasons. These instruments limit the Company's exposure to changes in the benchmark interest rate in the period from the trade date through the date of maturity. Interest rate swaps may be designated as cash flow hedges. The Company generally accounts for interest rate swaps at fair value and recognizes them in the balance sheet in prepaid expenses and other current assets or other current liabilities with changes in fair value recorded within AOCI. As of September 30, 2018 and December 31, 2017, the Company did not have any outstanding interest rate swaps.

Realized gains and losses from cash flow hedges are recorded in the statement of cash flows as a component of cash flows from operating activities. Subsequent to the issuance of each debt instrument, amounts remaining in AOCI are amortized over the life of the fixed-rate debt instrument. During the nine months ended September 30, 2018 and 2017, there were no unrealized gains or losses recorded within AOCI related to these instruments as they settled in 2015. For the three and nine months ended September 30, 2018, the Company reclassified interest rate swap losses of $52 thousand and $172 thousand, net of tax of $27 thousand and $66 thousand, respectively, into earnings. For the three and nine months ended September 30, 2017, the Company reclassified interest rate swap losses of $53 thousand and $160 thousand, net of tax of $31 thousand and $92 thousand, respectively, into earnings. As of September 30, 2018 and December 31, 2017, $1.2 million and $1.4 million, net of tax, respectively, remained in AOCI, related to these instruments.

10. Commitments and Contingencies

Aircraft-Related Commitments and Financing Arrangements

The Company’s contractual purchase commitments consist primarily of aircraft and engine acquisitions through manufacturers. During the first quarter of 2018, the Company negotiated revisions to its A320 aircraft order. The Company originally had 14 A320neo aircraft scheduled for delivery in 2019. Pursuant to the revisions, 5 of the 14 scheduled A320neo aircraft were converted to A320ceo aircraft and are scheduled to be delivered in the remainder of 2018 and 2019. During the third quarter of 2018, the Company entered into operating lease agreements for the lease of seven A320neos that are scheduled to be delivered in the remainder of 2018 and 2019. As of September 30, 2018, the Company's aircraft orders consisted of the following:

	Airbus		Third-Party Lessor
	A320ceo	A320neo	A320neo	Total
remainder of 2018	5		3	8
2019	2	9	4	15
2020		16		16
2021		18		18
	7	43	7	57

During the first quarter of 2018, the Company entered into an aircraft purchase agreement for the purchase of 14 A319 aircraft, which were previously financed under operating lease agreements. The contract was deemed a lease modification which resulted in a change of classification from operating leases to capital leases for the 14 aircraft. As a result, the Company recorded a short-term capital lease asset of $236.7 million within flight equipment and a short-term capital lease obligation of $143.8 million, net of the related maintenance reserves and security deposits, within current maturities of long-term debt and capital leases on the condensed balance sheet as of March 31, 2018. The purchase of all 14 aircraft was completed during the second quarter of 2018 for an aggregate gross purchase price of $285.0 million, which was comprised of cash payments, net of the application of cash maintenance and security deposits held by the previous lessor. For additional information, refer to Note 5, Special Charges.

18

Notes to Condensed Financial Statements—(Continued)

During the first quarter of 2018, the Company entered into an agreement to purchase six new engines. As of September 30, 2018, the Company had purchased all six engines, unencumbered. In addition, during the second quarter of 2018, the Company sold 5 used engines for $9.5 million at a loss of $4.4 million which is recorded within loss on disposal of assets in the statement of operations. The Company also has two spare engine orders for V2500 SelectTwo engines with International Aero Engines ("IAE") and nine spare engine orders for PurePower PW1100G-JM engines with Pratt & Whitney. Spare engines are scheduled for delivery from 2018 through 2023. Purchase commitments for these aircraft and engines, including estimated amounts for contractual price escalations and pre-delivery payments, are expected to be $210.2 million for the remainder of 2018, $592.1 million in 2019, $810.8 million in 2020, $775.4 million in 2021, $17.0 million in 2022, and $8.0 million in 2023 and beyond. As of September 30, 2018, the Company had secured debt financing commitments of $39.1 million for 1 aircraft, delivered in October 2018. In addition, the Company has secured financing for seven aircraft to be leased directly from a third-party lessor, scheduled for delivery in 2018 through 2019. Aircraft rent commitments for these 7 leased aircraft are expected to be approximately $1.0 million for the remainder of 2018, $27.2 million in 2019, $29.4 million in 2020, $29.4 million in 2021, $29.4 million in 2022, and $235.9 million in 2023 and beyond. As of September 30, 2018, the Company does not have financing commitments in place for the remaining 49 Airbus aircraft currently on firm order, which are scheduled for delivery in 2018 through 2021.

Interest commitments related to the secured debt financing of 55 delivered aircraft as of September 30, 2018 are $21.6 million for the remainder of 2018, $76.3 million in 2019, $69.7 million in 2020, $63.2 million in 2021, $56.8 million in 2022, and $179.4 million in 2023 and beyond. For principal commitments related to these financed aircraft, refer to Note 12, Debt and Other Obligations. As of September 30, 2018, principal and interest commitments related to the Company's future secured debt financing of 1 undelivered aircraft under the Series 2017-1 EETC are $0 for the remainder of 2018, $4.4 million in 2019, $4.0 million in 2020, $3.3 million in 2021, $3.1 million in 2022, and $34.0 million in 2023 and beyond.

As of September 30, 2018, the Company had a fleet consisting of 121 A320 family aircraft. As of September 30, 2018, this fleet was comprised of 44 aircraft financed under operating leases, with lease term expirations between 2021 and 2029, and 77 purchased aircraft, of which 22 were purchased off lease and are currently unencumbered. In addition, as of September 30, 2018, the Company had 12 spare engines financed under operating leases with lease term expiration dates ranging from 2019 to 2027, and owned 6 unencumbered spare engines of which 1 was purchased off lease. One of the Company's leased aircraft has variable rent payments, which fluctuate based on changes in London Interbank Offered Rate ("LIBOR"). The Company entered into sale leaseback transactions with third-party aircraft lessors for some of these aircraft and engine leases. Deferred losses resulting from these sale leaseback transactions are included in other long-term assets on the accompanying balance sheet. Deferred losses are recognized as an increase to rent expense on a straight-line basis over the term of the respective operating leases. Deferred gains are included in deferred gains and other long-term liabilities on the accompanying balance sheet. Deferred gains are recognized as a decrease to rent expense on a straight-line basis over the term of the respective operating leases.

Under the terms of the lease agreements, the Company will continue to operate and maintain the aircraft. Payments under the majority of the lease agreements are fixed for the term of the lease. The lease agreements contain standard termination events, including termination upon a breach of the Company's obligations to make rental payments and upon any other material breach of the Company's obligations under the leases, and standard maintenance and return condition provisions. These return provisions are evaluated at inception of the lease and throughout the lease terms and are accounted for as supplemental rent expense when it is probable that such amounts will be incurred. Upon a termination of the lease due to a breach by the Company, the Company would be liable for standard contractual damages, possibly including damages suffered by the lessor in connection with remarketing the aircraft or while the aircraft is not leased to another party.

In July 2015, the Company executed an upgrade service agreement with Airbus Americas Customer Services Inc. ("Airbus") to reconfigure the seating and increase capacity in 40 of the Company’s A320ceos from 178 to 182 seats ("reconfiguration"). The reconfiguration of the aircraft commenced in the first quarter of 2016 and was completed in the second quarter of 2018. As of September 30, 2018, the Company had no further commitments related to this agreement. The amounts related to the reconfiguration are capitalized within flight equipment on the balance sheet.

19

Notes to Condensed Financial Statements—(Continued)

Future minimum lease payments under capital leases and noncancellable operating leases at September 30, 2018 were as follows: 

		Capital Leases		Aircraft and Spare Engine Operating Leases		Property Facility Operating Leases		Total Operating and Capital Lease Obligations
	(in thousands)
remainder of 2018		$	165	$	42,762	$	15,122	$	58,049
2019		625		167,360		45,018		213,003
2020		249		161,876		29,636		191,761
2021		28		160,185		16,645		176,858
2022		—		146,904		14,403		161,307
2023 and thereafter		—		419,925		101,897		521,822
Total minimum lease payments		$	1,067	$	1,099,012	$	222,721	$	1,322,800
Less amount representing interest		49
Present value of minimum lease payments		$	1,018
Less current portion		596
Long-term portion		$	422

The majority of the Company's capital lease obligations relate to the lease of computer equipment used by the Company's flight crew. Payments related to the lease of computer equipment are fixed for the 3-year term of the lease.

Aircraft rent expense consists of monthly lease rents for aircraft and spare engines under the terms of the Company's aircraft and spare engine lease agreements recognized on a straight-line basis. Aircraft rent expense also includes supplemental rent. Supplemental rent is made up of maintenance reserves paid or expected to be paid to aircraft lessors in advance of the performance of major maintenance activities that are not probable of being reimbursed, and probable and estimable return condition obligations. The Company expects supplemental rent to increase as individual aircraft lease agreements approach their respective termination dates and the Company begins to accrue the estimated cost of return conditions for the corresponding aircraft.

Some of the Company’s aircraft and engine master lease agreements provide that the Company pays maintenance reserves to aircraft lessors to be held as collateral in advance of the Company’s required performance of major maintenance activities. A majority of these maintenance reserve payments are calculated based on a utilization measure, such as flight hours or cycles, while some maintenance reserve payments are fixed, time-based contractual amounts. Fixed maintenance reserve payments for these aircraft and related flight equipment, including estimated amounts for contractual price escalations, are expected to be $1.8 million for the remainder of 2018, $5.8 million in 2019, $5.6 million in 2020, $5.7 million in 2021, $4.9 million in 2022, and $12.9 million in 2023 and beyond. These lease agreements generally provide that maintenance reserves are reimbursable to the Company upon completion of the maintenance event. Some of the master lease agreements do not require that the Company pay maintenance reserves so long as the Company's cash balance does not fall below a certain level. As of September 30, 2018, the Company is in full compliance with those requirements and does not anticipate having to pay reserves related to these master leases in the future.

The Company is contractually obligated to pay the following minimum guaranteed payments for its reservation system and other miscellaneous subscriptions and services as of September 30, 2018: $2.5 million for the remainder of 2018, $12.6 million in 2019, $12.7 million in 2020, $9.9 million in 2021, $10.0 million in 2022, and $66.6 million thereafter. During the first quarter of 2018, the Company entered into a contract renewal with its reservation system provider which expires in 2028.

Litigation

The Company is subject to commercial litigation claims and to administrative and regulatory proceedings and reviews that may be asserted or maintained from time to time. The Company believes the ultimate outcome of such lawsuits, proceedings and reviews will not, individually or in the aggregate, have a material adverse effect on its financial position, liquidity or results of operations.

20

Notes to Condensed Financial Statements—(Continued)

Credit Card Processing Arrangements

The Company has agreements with organizations that process credit card transactions arising from the purchase of air travel, baggage charges, and other ancillary services by customers. As is standard in the airline industry, the Company's contractual arrangements with credit card processors permit them, under certain circumstances, to retain a holdback or other collateral, which the Company records as restricted cash, when future air travel and other future services are purchased via credit card transactions. The required holdback is the percentage of the Company's overall credit card sales that its credit card processors hold to cover refunds to customers if the Company fails to fulfill its flight obligations.

The Company's credit card processors do not require the Company to maintain cash collateral provided that the Company satisfies certain liquidity and other financial covenants. Failure to meet these covenants would provide the processors the right to place a holdback resulting in a commensurate reduction of unrestricted cash. As of September 30, 2018 and December 31, 2017, the Company was in compliance with such liquidity and other financial covenants in its credit card processing agreements and the processors were holding back no remittances.

The maximum potential exposure to cash holdbacks by the Company's credit card processors, based upon advance ticket sales and $9 Fare Club memberships as of September 30, 2018 and December 31, 2017, was $341.5 million and $286.3 million, respectively.

Employees

The Company has 4 union-represented employee groups that together represented approximately 76% of all employees at September 30, 2018. The table below sets forth the Company's employee groups and status of the collective bargaining agreements as of September 30, 2018.

Employee Groups	Representative	Amendable Date	Percentage of Workforce
Pilots	Air Line Pilots Association, International ("ALPA")	February 2023	27%
Flight Attendants	Association of Flight Attendants ("AFA-CWA")	May 2021	44%
Dispatchers	Professional Airline Flight Control Association ("PAFCA")	October 2023	1%
Ramp Service Agents	International Association of Machinists and Aerospace Workers ("IAMAW")	June 2020	4%

In August 2015, the Company's collective bargaining agreement with its pilots, represented by ALPA, became amendable. In June 2016, ALPA requested the services of the National Mediation Board ("NMB") to facilitate negotiations for an amended agreement and the Company joined ALPA in the request. In January 2018, under the guidance of the NMB assigned mediators, the parties reached a tentative agreement. In February 2018, the pilot group voted to approve the new five-year agreement with the Company. The new agreement includes a one-time ratification incentive and other negotiated contractual provisions which were recorded in special charges (credits) within operating expenses in the condensed statement of operations for the nine months ended September 30, 2018. For additional information, refer to Note 5, Special Charges.

In December 2017, the Professional Airline Flight Control Association ("PAFCA") filed an application with the NMB seeking to represent the Company's dispatchers, who were previously represented by the Transport Workers Union ("TWU"). In January 2018, the NMB determined that a representation election would be held. The voting period for the representation election took place through February 20, 2018 and the dispatchers elected to be represented by the PAFCA. In June 2018, the Company commenced negotiations with PAFCA for an amended agreement with its dispatchers. In October 2018, PAFCA and the Company reached a tentative agreement for a new five-year agreement, which was ratified by the PAFCA members on October 17, 2018. The terms of the new agreement are currently in effect.

In June 2018, the NMB notified the Company that the TWU filed an application seeking a representation election for the Company's passenger service agents. The NMB determined that a representation election would be held and the voting period for the election took place through September 4, 2018. The Company’s passenger service agents voted to be represented by the TWU, but the representation applies only to the Company’s Fort Lauderdale station where the Company has direct employees in the passenger service classification. The Company and the TWU will meet in late October 2018 to begin negotiating a collective bargaining agreement.

The Company is self-insured for health care claims, up to a stop loss amount for eligible participating employees and qualified dependent medical claims, subject to deductibles and limitations. The Company’s liabilities for claims incurred but not reported are determined based on an estimate of the ultimate aggregate liability for claims incurred. The estimate is

21

Notes to Condensed Financial Statements—(Continued)

calculated from actual claim rates and adjusted periodically as necessary. The Company has accrued $5.6 million and $3.9 million in health care claims as of September 30, 2018 and December 31, 2017, respectively.

11. Fair Value Measurements

Under ASC 820, "Fair Value Measurements and Disclosures", disclosures relating to how fair value is determined for assets and liabilities are required, and a hierarchy for which these assets and liabilities must be grouped is established, based on significant levels of inputs, as follows:

Level 1—Quoted prices in active markets for identical assets or liabilities.

Level 2—Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The Company utilizes several valuation techniques in order to assess the fair value of the Company’s financial assets and liabilities.

Fuel Derivative Instruments

From time to time, the Company may enter into fuel derivative contracts in order to mitigate the risk of future volatility in fuel prices. The Company’s fuel derivative contracts generally consist of jet fuel swaps and jet fuel options. These instruments are valued using energy and commodity market data, which is derived by combining raw inputs with quantitative models and processes to generate forward curves and volatilities.

The Company utilizes the market approach to measure fair value for its fuel derivative instruments, if any. The market approach uses prices and other relevant information generated by market transactions involving identical or comparable assets or liabilities.

The Company has not historically elected hedge accounting on its fuel derivative instruments, if any. As a result, the Company would record the fair value adjustment of any fuel derivatives in the accompanying statement of operations within aircraft fuel and on the balance sheet within prepaid expenses and other current assets or other current liabilities, depending on whether the net fair value of the derivatives is in an asset or liability position as of the respective date. Fair values of any fuel derivative instruments are determined using standard option valuation models. The Company also considers counterparty risk and its own credit risk in its determination of all estimated fair values. The Company offsets fair value amounts recognized for any derivative instruments executed with the same counterparty under a master netting arrangement. The Company determines fair value of any jet fuel options utilizing an option pricing model based on inputs that are either readily available in public markets or can be derived from information available in publicly quoted markets. The Company has consistently applied these valuation techniques in all periods presented and believes it has obtained the most accurate information available for the types of derivative contracts it holds.

The fair value of the Company's jet fuel swaps, if any, are determined based on inputs that are readily available in public markets or can be derived from information available in publicly quoted markets; therefore, the Company categorizes these instruments as Level 2. Due to the fact that certain inputs utilized to determine the fair value of jet fuel options are unobservable (principally implied volatility), the Company categorizes these derivatives as Level 3. Implied volatility of a jet fuel option is the volatility of the price of the underlying commodity that is implied by the market price of the option based on an option pricing model. Thus, it is the volatility that when used in a particular pricing model yields a theoretical value for the option equal to the current market price of that option. Implied volatility, a forward-looking measure, differs from historical volatility because the latter is calculated from known past returns. At each balance sheet date, the Company substantiates and adjusts unobservable inputs. The Company routinely assesses the valuation model's sensitivity to changes in implied volatility. As of September 30, 2018 and December 31, 2017, the Company had no outstanding jet fuel derivatives.

Long-Term Debt

The estimated fair value of the Company's term loan debt agreements has been determined to be Level 3 as certain inputs used to determine the fair value of these agreements are unobservable. The Company utilizes a discounted cash flow method to estimate the fair value of the Level 3 long-term debt. The estimated fair value of the Company's publicly and non-

22

Notes to Condensed Financial Statements—(Continued)

publicly held EETC debt agreements has been determined to be Level 2 as the Company utilizes quoted market prices in markets with low trading volumes to estimate the fair value of its Level 2 long-term debt.

The carrying amounts and estimated fair values of the Company's long-term debt at September 30, 2018 and December 31, 2017 were as follows:

	September 30, 2018				December 31, 2017				Fair Value Level Hierarchy
	Carrying Value		Estimated Fair Value		Carrying Value		Estimated Fair Value
	(in millions)
Senior term loans	$	391.4	$	395.5	$	417.9	$	435.3	Level 3
Junior term loans	33.2		33.6		39.3		40.4		Level 3
Fixed-rate loans	493.9		487.2		518.0		528.6		Level 3
2015-1 EETC Class A	393.6		389.8		408.6		420.9		Level 2
2015-1 EETC Class B	84.0		83.5		92.0		94.2		Level 2
2015-1 EETC Class C	115.2		114.4		—		—		Level 2
2017-1 EETC Class AA	223.3		213.6		37.5		37.4		Level 2
2017-1 EETC Class A	74.4		71.1		12.5		12.6		Level 2
2017-1 EETC Class B	76.7		73.3		13.8		13.8		Level 2
2017-1 EETC Class C	78.9		78.3		—		—		Level 2
Total long-term debt	$	1,964.6	$	1,940.3	$	1,539.6	$	1,583.2

Cash and Cash Equivalents

Cash and cash equivalents at September 30, 2018 and December 31, 2017 are comprised of liquid money market funds and cash, and are categorized as Level 1 instruments. The Company maintains cash with various high-quality financial institutions.

Short-term Investment Securities

Short-term investment securities at September 30, 2018 and December 31, 2017 are classified as available-for-sale and consist of U.S. Treasury and U.S. government agency securities with contractual maturities of 12 months or less. The Company's short-term investment securities are categorized as Level 1 instruments, as the Company uses quoted market prices in active markets when determining the fair value of these securities. For additional information, refer to Note 7, Short-term Investment Securities.

Assets and liabilities measured at gross fair value on a recurring basis are summarized below:

	Fair Value Measurements as of September 30, 2018
	Total		Level 1		Level 2		Level 3
	(in millions)
Cash and cash equivalents	$	773.7	$	773.7	$	—	$	—
Short-term investment securities	102.2		102.2		—		—
Total assets	$	875.9	$	875.9	$	—	$	—
Total liabilities	$	—	$	—	$	—	$	—

23

Notes to Condensed Financial Statements—(Continued)

	Fair Value Measurements as of December 31, 2017
	Total		Level 1		Level 2		Level 3
	(in millions)
Cash and cash equivalents	$	800.8	$	800.8	$	—	$	—
Short-term investment securities	100.9		100.9		—		—
Total assets	$	901.7	$	901.7	$	—	$	—
Total liabilities	$	—	$	—	$	—	$	—

The Company had no transfers of assets or liabilities between any of the above levels during the periods ended September 30, 2018 and December 31, 2017.

The Company's Valuation Group, which reports to the Chief Financial Officer, is made up of individuals from the Company's Treasury and Corporate Accounting departments. The Valuation Group is responsible for the execution of the Company's valuation policies and procedures. The Valuation Group compares the results of the Company's internally developed valuation methods with counterparty reports at each balance sheet date, assesses the Company's valuation methods for accurateness and identifies any needs for modification.

12. Debt and Other Obligations

As of September 30, 2018, the Company had outstanding non-public and public debt instruments. During the nine months ended September 30, 2018, the Company issued additional debt through the 2015-1 and 2017-1 EETCs described below.

2017-1 Class AA, Class A and Class B EETCs

In November 2017, the Company created three separate pass-through trusts, which issued $420.5 million aggregate face amount of Series 2017-1 Class AA, Class A and Class B EETCs in connection with the financing of 7 new Airbus A320 aircraft and 5 new Airbus A321 aircraft. Each class of certificates represents a fractional undivided interest in the respective pass-through trusts and is not an obligation of the Company. The proceeds from the issuance of these certificates are initially held in escrow by a depositary and, upon satisfaction of certain terms and conditions, are released and used to purchase equipment notes which are issued by the Company and secured by the Company's aircraft. Interest on the issued and outstanding equipment notes is payable semiannually on February 15 and August 15 of each year, commencing on August 15, 2018, and principal on such equipment notes is scheduled for payment on February 15 and August 15 of certain years. Principal payments commenced on August 15, 2018 in the case of five new Airbus A321 aircraft delivered from February 2018 to March 2018 and three Airbus A320 aircraft delivered from December 2017 to January 2018 and will commence on February 15, 2019 for three Airbus A320 aircraft delivered from April 2018 to August 2018 and one Airbus A320 aircraft scheduled for delivery in October 2018. Issued and outstanding Series AA and Series A equipment notes mature in February 2030 and Series B equipment notes mature in February 2026. Issued and outstanding Series AA, Series A and Series B equipment notes accrue interest at a rate of 3.375%, 3.650% and 3.800%, respectively. As of September 30, 2018, $388.0 million of the proceeds from the sale of the Series 2017-1 Class AA, Class A and Class B EETCs had been used to purchase equipment notes in connection with the financing of five Airbus A321 aircraft and six Airbus A320 aircraft. The remaining $32.5 million of escrowed proceeds held by the pass-through trusts will be used to purchase equipment notes as the remaining one new aircraft is delivered in October 2018. Equipment notes that are issued are reported as debt on the Company's condensed balance sheets.

2015-1C and 2017-1C EETCs

In May 2018, the Company completed a private placement of an aggregate amount of $115.2 million pass-through certificates, Series 2015-1C. The Company entered into 15 separate participation agreement amendments to existing participation agreements that were entered into by the Company during the period from October 2015 to February 2017 under the existing pass through trust formed by the Company on August 11, 2015. The Series 2015-1C equipment notes are secured by 12 Airbus A321 aircraft previously delivered from October 2015 to January 2017 and 3 Airbus A320 aircraft previously delivered from March 2016 to June 2016. The Series 2015-1C equipment notes mature in April 2023 and accrue interest at a

24

Notes to Condensed Financial Statements—(Continued)

rate of 4.93%. Principal and interest on the issued and outstanding Series 2015-1C equipment notes is payable semiannually on April 1 and October 1 of each year, commencing on October 1, 2018. Equipment notes that are issued are reported as debt on the Company's condensed balance sheets.

In May 2018, the Company also completed a private placement of an aggregate amount of $85.5 million pass-through certificates, Series 2017-1C. The Company entered into 9 separate participation agreement amendments to existing participation agreements that were entered into by the Company during the period from December 2017 to April 2018 under the existing pass through trust formed by the Company on November 28, 2017. The participation agreement amendments provide for the issuance of series 2017-1C equipment notes, in the aggregate principal amount of $65.7 million in connection with previously delivered aircraft. The 2017-1C equipment notes are secured by five Airbus A321 aircraft previously delivered from February 2018 to March 2018 and four Airbus A320 aircraft previously delivered from December 2017 to April 2018. The Series 2017-1C equipment notes mature in February 2023 and accrue interest at a rate of 5.11%. Interest on the Class C 2017-1 issued and outstanding equipment notes are payable semiannually on February 15 and August 15 of each year, commencing on August 15, 2018. The entire principal on the issued and outstanding Series 2017-1C equipment notes is scheduled for payment on February 15, 2023. As of September 30, 2018, $13.2 million of the proceeds from the sale of the Series 2017-1 Class C had been used to purchase equipment notes in connection with the financing of two Airbus A320 aircraft. The remaining $6.6 million of escrowed proceeds held by the pass-through trusts will be used to purchase equipment notes when the remaining 1 Airbus A320 aircraft is delivered in October 2018. Equipment notes that are issued are reported as debt on the Company's condensed balance sheets.

The Company evaluated whether the pass-through trusts formed are variable interest entities ("VIEs") required to be consolidated by the Company under applicable accounting guidance. The Company determined that the pass-through trusts are VIEs and that it does not have a variable interest in the pass-through trusts. Based on this analysis, the Company determined that it is not required to consolidate these pass-through trusts.

Long-term debt is comprised of the following:

	As of				Three Months Ended September 30,				Nine Months Ended September 30,
	September 30, 2018		December 31, 2017		2018		2017		2018		2017
	(in millions)				(weighted-average interest rates)
Fixed-rate senior term loans due through 2027	$	391.4	$	417.9	4.10	%	4.10	%	4.10	%	4.10	%
Fixed-rate junior term loans due through 2022	33.2		39.3		6.90	%	6.90	%	6.90	%	6.90	%
Fixed-rate loans due through 2029	493.9		518.0		3.83	%	3.76	%	3.83	%	3.76	%
Fixed-rate class A 2015-1 EETC due through 2028	393.6		408.6		4.10	%	4.10	%	4.10	%	4.10	%
Fixed-rate class B 2015-1 EETC due through 2024	84.0		92.0		4.45	%	4.45	%	4.45	%	4.45	%
Fixed-rate class C 2015-1 EETC due through 2023	115.2		—		4.93	%	N/A		4.93	%	N/A
Fixed-rate class AA 2017-1 EETC due through 2030	223.3		37.5		3.38	%	N/A		3.38	%	N/A
Fixed-rate class A 2017-1 EETC due through 2030	74.4		12.5		3.65	%	N/A		3.65	%	N/A
Fixed-rate class B 2017-1 EETC due through 2026	76.7		13.8		3.80	%	N/A		3.80	%	N/A
Fixed-rate class C 2017-1 EETC due through 2023	78.9		—		5.11	%	N/A		5.11	%	N/A
Long-term debt	1,964.6		1,539.6
Less current maturities	150.2		115.4
Less unamortized discounts	43.9		36.7
Total	$	1,770.5	$	1,387.5

During the three and nine months ended September 30, 2018, the Company made scheduled principal payments of $32.6 million and $93.2 million on its outstanding debt obligations, respectively. During the three and nine months ended September 30, 2017, the Company made scheduled principal payments of $13.4 million and $63.4 million on its outstanding debt obligations, respectively.

At September 30, 2018, long-term debt principal payments for the next five years and thereafter are as follows:

25

Notes to Condensed Financial Statements—(Continued)

	September 30, 2018
	(in millions)
remainder of 2018	$	44.0
2019	158.3
2020	155.3
2021	151.0
2022	147.9
2023 and beyond	1,308.1
Total debt principal payments	$	1,964.6

Interest Expense

Interest expense related to long-term debt consisted of the following:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
	(in thousands)
Senior term loans	$	4,195	$	4,564	$	12,769	$	13,854
Junior term loans	605		746		1,908		2,323
Fixed-rate loans	4,844		2,811		14,636		4,555
Class A 2015-1 EETC	4,057		4,366		12,214		12,995
Class B 2015-1 EETC	939		1,118		2,881		3,410
Class C 2015-1 EETC	1,420		—		2,209		—
Class AA 2017-1 EETC	1,751		—		4,008		—
Class A 2017-1 EETC	631		—		1,445		—
Class B 2017-1 EETC	700		—		1,636		—
Class C 2017-1 EETC	934		—		1,400		—
Commitment fees	50		29		153		87
Amortization of debt discounts	1,784		1,362		4,930		3,883
Total	$	21,910	$	14,996	$	60,189	$	41,107

26

Notes to Condensed Financial Statements—(Continued)

13. Subsequent Events

On October 23, 2018, the Company entered into a revolving credit facility for up to $160 million secured by the collateral assignment of certain of the Company's rights under the Company's purchase agreement with Airbus, related to 43 Airbus A320neo aircraft scheduled to be delivered between August 2019 and December 2021. The Company intends to use any proceeds for working capital, capital expenditures and other general corporate purposes. The final maturity of the facility is December 30, 2020. As of October 24, 2018, no amounts have been drawn. Any drawdowns on the facility are subject to certain terms and conditions.

27

ITEM 2. MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS

Forward-Looking Statements

This Quarterly Report on Form 10-Q contains forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended (the "Securities Act"), and Section 21E of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), which are subject to the “safe harbor” created by those sections. Forward-looking statements are based on our management’s beliefs and assumptions and on information currently available to our management. All statements other than statements of historical factors are “forward-looking statements” for purposes of these provisions. In some cases, you can identify forward-looking statements by terms such as “may,” “will,” “should,” “could,” “would,” “expect,” “plan,” “anticipate,” “believe,” “estimate,” “project,” “predict,” “potential,” and similar expressions intended to identify forward-looking statements. Such forward-looking statements are subject to risks, uncertainties and other important factors that could cause actual results and the timing of certain events to differ materially from future results expressed or implied by such forward-looking statements. Factors that could cause or contribute to such differences include, but are not limited to, those identified below, and those discussed in the section titled “Risk Factors” in this report and in Item 1A "Risk Factors" in our Annual Report on Form 10-K for the year ended December 31, 2017 and subsequent Quarterly Reports on Form 10-Q. Furthermore, such forward-looking statements speak only as of the date of this report. Except as required by law, we undertake no obligation to update any forward-looking statements to reflect events or circumstances after the date of such statements.

Overview

Spirit Airlines, headquartered in Miramar, Florida, offers affordable travel to value-conscious customers. Our all-Airbus fleet is one of the youngest and most fuel efficient in the United States. We currently operate more than 500 daily flights to 69 destinations in 16 countries throughout the United States, Latin America and the Caribbean, including 9 new cities opened in 2018. Our stock trades under the symbol "SAVE" on the New York Stock Exchange ("NYSE").

We focus on value-conscious travelers who pay for their own travel, and our business model is designed to deliver what our customers want: low fares and a great experience. We compete based on total price. We allow our customers to see all available options and their respective prices prior to purchasing a ticket, and this full transparency illustrates that our total price, including options selected, is lower on average than other airlines. By offering customers unbundled base fares, we give customers the power to save by paying only for the Á La Smarte options they choose, such as checked and carry-on bags and advance seat assignments. We record revenue related to these options as non-fare passenger revenue, which is recorded within passenger revenues in our statement of operations.

We use low fares to address underserved markets, which helps us to increase passenger volume, load factors and non-ticket revenue on the flights we operate. We also have high-density seating configurations on our aircraft and a simplified onboard product designed to lower costs. High passenger volumes and load factors help us sell more ancillary products and services, which in turn allows us to reduce our fares even further.

We continue our commitment to delivering the best value in the sky by continuing to make improvements to the customer experience. Our new mobile-friendly website makes booking easier. Our new mobile application allows check-in while on the go, and our airport kiosks and self bag-tagging help customers move through the airport more quickly.

Comparative Operating Statistics:

The following tables set forth our operating statistics for the three and nine-month period ended September 30, 2018 and 2017:

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	Three Months Ended September 30,				Percent Change
	2018		2017
Operating Statistics (unaudited) (A):
Average aircraft	119.8		105.5		13.6	%
Aircraft at end of period	121		107		13.1	%
Average daily aircraft utilization (hours)	12.4		11.6		6.9	%
Average stage length (miles)	1,033		1,006		2.7	%
Block hours	136,723		112,701		21.3	%
Departures	50,386		42,599		18.3	%
Passenger flight segments (PFSs) (thousands)	7,856		6,307		24.6	%
Revenue passenger miles (RPMs) (thousands)	8,241,771		6,452,529		27.7	%
Available seat miles (ASMs) (thousands)	9,579,448		7,681,312		24.7	%
Load factor (%)	86.0	%	84.0	%	2.0 pts
Fare revenue per passenger flight segment ($)	60.67		56.38		7.6	%
Non-ticket revenue per passenger flight segment ($)	54.44		52.58		3.5	%
Total revenue per passenger flight segment ($)	115.11		108.96		5.6	%
Average yield (cents)	10.97		10.65		3.0	%
TRASM (cents)	9.44		8.95		5.5	%
CASM (cents)	7.93		7.59		4.5	%
Adjusted CASM (cents)	7.92		7.49		5.7	%
Adjusted CASM ex-fuel (cents)	5.22		5.42		(3.7	)%
Fuel gallons consumed (thousands)	109,515		90,274		21.3	%
Average economic fuel cost per gallon ($)	2.36		1.75		34.9	%

(A) See "Glossary of Airline Terms" elsewhere in this quarterly report for definitions used in this table. Certain prior period statistics reflect adjustments after the adoption of ASU 2014-09, "Revenue from Contracts with Customers".

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	Nine Months Ended September 30,				Percent Change
	2018		2017
Operating Statistics (unaudited) (A):
Average aircraft	117.5		101.9		15.3	%
Aircraft at end of period	121		107		13.1	%
Average daily aircraft utilization (hours)	12.3		11.7		5.1	%
Average stage length (miles)	1,037		991		4.6	%
Block hours	396,034		326,033		21.5	%
Departures	144,772		123,492		17.2	%
Passenger flight segments (PFSs) (thousands)	21,947		18,083		21.4	%
Revenue passenger miles (RPMs) (thousands)	23,016,417		18,285,588		25.9	%
Available seat miles (ASMs) (thousands)	27,504,053		21,851,789		25.9	%
Load factor (%)	83.7	%	83.7	%	0 pts
Fare revenue per passenger flight segment ($)	57.36		56.74		1.1	%
Non-ticket revenue per passenger flight segment ($)	54.74		52.61		4.0	%
Total revenue per passenger flight segment ($)	112.10		109.35		2.5	%
Average yield (cents)	10.69		10.81		(1.1	)%
TRASM (cents)	8.95		9.05		(1.1	)%
CASM (cents)	8.16		7.71		5.8	%
Adjusted CASM (cents)	7.82		7.63		2.5	%
Adjusted CASM ex-fuel (cents)	5.24		5.62		(6.8	)%
Fuel gallons consumed (thousands)	310,661		254,871		21.9	%
Average economic fuel cost per gallon ($)	2.28		1.73		31.8	%

(A) See "Glossary of Airline Terms" elsewhere in this quarterly report for definitions used in this table. Certain prior period statistics reflect adjustments after the adoption of ASU 2014-09, "Revenue from Contracts with Customers".

Critical Accounting Policies and Estimates    

Except as set forth below, for information regarding our Critical Accounting Policies and Estimates, see the "Critical Accounting Policies and Estimates" section of "Item 7. Management's Discussion and Analysis of Financial Condition and Results of Operations" in our Form 10-K.

Passenger revenues

Fare revenues. Tickets sold are initially deferred as “air traffic liability.” Passenger fare revenues are recognized at time of departure when transportation is provided. All tickets sold are nonrefundable. An unused ticket expires at the date of scheduled travel and is recognized as revenue at the date of scheduled travel. Passenger revenues reported prior to the adoption of ASU 2014-09 are now reported as fare revenues within passenger revenues in our disaggregated revenue table within Note 4, Revenue Disaggregation.

As of December 31, 2017 and 2016, we had air traffic liability balances of $263.7 million and $220.2 million, respectively. As of September 30, 2018, all of the ATL balance as of December 31, 2017 has been recognized.

Non-fare revenues.The adoption of ASU 2014-09 impacted the classification of certain ancillary items such as bags, seats and other travel-related fees, since they are deemed part of the single performance obligation of providing passenger transportation. These ancillary items are now recognized in non-fare revenues within passenger revenues in our disaggregated revenue table within Note 4, Revenue Disaggregation.

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Changes and cancellations. Customers may elect to change or cancel their itinerary prior to the date of departure. For changes, a service charge is recognized at time of departure of newly scheduled travel and is deducted from the face value of the original purchase price of the ticket, and the original ticket becomes invalid. For cancellations, a service charge is assessed and the amount remaining after deducting the service charge is called a credit shell which generally expires 60 days from the date the credit shell is created and can be used towards the purchase of a new ticket and other service offerings. Both the service charge and credit shell amounts are recorded as deferred revenue and amounts expected to expire unused are estimated based on historical experience. Estimating the amount of credits that will go unused involves some level of subjectivity and judgment. However, given the relatively short period of time to expiration, this does not have a significant impact on our financial statements.

Other revenues

Other revenues primarily consist of the marketing component of the sale of frequent flyer miles to our credit card partner and commissions revenue from the sale of various items such as hotels and rental cars.

Frequent Flyer Program

Our frequent flyer program generates customer loyalty by rewarding customers with mileage credits to travel on Spirit. When traveling, customers earn redeemable mileage credits for each mile flown on Spirit. Customers can also earn mileage credits through participating companies such as our co-branded Spirit credit card. Mileage credits are redeemable by customers in future periods for air travel on Spirit.

To reflect the mileage credits earned, the program includes two types of transactions that are considered revenue arrangements with multiple performance obligations: (1) mileage credits earned with travel and (2) mileage credits sold to co-branded credit card partner.

The adoption of ASU 2014-09 eliminated the incremental cost method for frequent flier program accounting, which required us to re-value and record a liability associated with customer flight miles earned with travel as part of our frequent flier program with a relative fair value. Upon adoption of ASU 2014-09 on January 1, 2018, we recorded an increase to air traffic liability of $12.4 million.

Passenger ticket sales earning mileage credits. Passenger ticket sales earning mileage credits provide customers with (1) mileage credits earned and (2) air transportation. We value each performance obligation on a standalone basis. To value the mileage credits earned, we consider the quantitative value a passenger receives by redeeming miles for a ticket rather than paying cash, which is referred to as equivalent ticket value ("ETV").

We defer revenue for the mileage credits when earned and recognize loyalty travel awards in passenger revenue as the miles are redeemed and services are provided. We record the air transportation portion of the passenger ticket sales in air traffic liability and recognize passenger revenue when we provide transportation or if the ticket goes unused.

Sale of mileage credits. Customers may earn mileage credits based on their spending with our co-branded credit card company with which we have an agreement to sell mileage credits. Our contract to sell mileage credits under this agreement has multiple performance obligations. During the nine months ended September 30, 2018 and 2017, total cash sales from this agreement were $29.6 million and $38.1 million, respectively, which are allocated to travel and other performance obligations, as discussed below.

Our co-brand credit card agreement provides for joint marketing where cardholders earn mileage credits for making purchases using co-branded cards. During 2015, we extended our agreement with the administrator of the FREE SPIRIT affinity credit card program to extend through 2022. We account for this agreement consistently with the accounting method that allocates the consideration received to the individual products and services delivered. We allocate the value based on the relative selling prices of those products and services, which generally consists of (i) travel miles to be awarded, (ii) licensing of brand and access to member lists and (iii) advertising and marketing efforts. We determined our best estimate of the selling prices by considering discounted cash flow analysis using multiple inputs and assumptions, including: (1) the expected number of miles awarded and number of miles redeemed, (2) ETV for the award travel obligation, (3) licensing of brand and access to member lists and (4) advertising and marketing efforts. 

We defer the amount for award travel obligation as part of loyalty deferred revenue within air traffic liability on the balance sheet and recognize loyalty travel awards in passenger revenue as the mileage credits are used for travel. Revenue

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allocated to the remaining performance obligations, primarily marketing components, is recorded in other revenue over time as miles are delivered.

Mileage breakage. For mileage credits that we estimate are not likely to be redeemed ("breakage"), we recognize the associated value proportionally during the period in which the remaining mileage credits are redeemed. Management uses statistical models to estimate breakage based on historical redemption patterns. A change in assumptions as to the period over which mileage credits are expected to be redeemed, the actual redemption activity for mileage credits or the estimated fair value of mileage credits expected to be redeemed could have an impact on our revenue in the year in which the change occurs and in future years.

Current activity of frequent flyer program. Mileage credits are combined in one homogeneous pool and are not separately identifiable. As such, revenue is comprised of miles that were part of the frequent flyer deferred revenue balance at the beginning of the period as well as miles that were issued during the period.

Executive Summary

For the third quarter of 2018, we achieved a 16.0% operating margin, an increase of 0.9 point compared to the prior year period. We generated pre-tax income of $128.6 million and net income of $97.5 million on operating revenues of $904.3 million. For the third quarter of 2017, we generated pre-tax income of $94.6 million and net income of $60.0 million on operating revenues of $687.2 million.

Our adjusted CASM ex-fuel for the third quarter of 2018 was 5.22 cents, a 3.7% decrease year over year. The decrease on a per-ASM basis was primarily due to decreases in aircraft rent expense and other operating expense.

As of September 30, 2018, we had 121 Airbus A320-family aircraft in our fleet comprised of 31 A319s, 55 A320s, 30 A321s, and 5 A320neos. With the scheduled delivery of 8 aircraft during the remainder of 2018, we expect to end 2018 with 129 aircraft in our fleet.

Since the delivery of our initial five A320neo aircraft in the fourth quarter of 2016, we have experienced introductory issues with the new-generation PW1100G-JM engines, which has resulted in diminished service availability of such aircraft. We continuously work with Pratt & Whitney to secure support and relief in connection with possible engine related operation disruptions.

Comparison of three months ended September 30, 2018 to three months ended September 30, 2017

Operating Revenues

Operating revenues increased $217.1 million, or 31.6%, to $904.3 million for the third quarter of 2018, as compared to the third quarter of 2017, primarily due to an increase in traffic of 27.7%, an increase in passenger yields of 3.0% and a load factor increase of 200 basis points.

Total revenue per available seat mile ("TRASM") for the third quarter of 2018 was 9.44 cents, an increase of 5.5%, as compared to the third quarter of 2017. This increase was due to higher passenger yields and higher load factor, year over year. The increase in average yield was driven by our strategic network re-orientation, improved yield management process and non-ticket revenue initiatives.

Total revenue per passenger flight segment increased 5.6%, year over year. Fare revenue per passenger flight segment increased 7.6% and non-ticket revenue per passenger flight segment increased 3.5%. The increase in fare revenue per passenger flight segment was driven by a 3.0% increase in average yield, period over period. The increase in non-ticket revenue per passenger flight segment was primarily attributable to higher bag revenue, passenger usage fee, and seat revenue per flight segment, as compared to the prior year.

Operating Expenses

Operating expenses increased $175.9 million, or 30.1%, to $759.2 million for the third quarter of 2018 compared to $583.4 million for the third quarter of 2017, primarily due to an increase in operations as reflected by a 24.7% capacity growth

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and a 27.7% increase in traffic. Furthermore, operating expenses increased as a result of higher aircraft fuel expense, year over year.

Aircraft fuel expense includes into-plane fuel expense (defined below) and realized and unrealized gains and losses associated with our fuel derivative contracts, if any. Into-plane fuel expense is defined as the price that we generally pay at the airport, including taxes and fees. Into-plane fuel prices are affected by the global oil market, refining costs, taxes and fees, which can vary by region in the United States and other countries where we operate. Into-plane fuel expense approximates cash paid to the supplier and does not reflect the effect of any fuel derivatives. From time to time, we may enter into fuel derivative contracts to protect the refining price risk between the price of crude oil and the price of refined jet fuel. We had no activity related to fuel derivative instruments during the three months ended September 30, 2018 and 2017. Historically, management has chosen not to elect hedge accounting on any fuel derivative instruments and, as a result, changes in the fair value of fuel derivative contracts have been recorded each period in aircraft fuel expense.

Aircraft fuel expense increased in the third quarter of 2018 by $100.5 million, or 63.5%, from $158.3 million in the third quarter of 2017 to $258.8 million in the third quarter of 2018. This higher fuel expense, year over year, was due to a 34.9% increase in average economic fuel cost per gallon and a 21.3% increase in fuel gallons consumed.

The elements of the changes in aircraft fuel expense are illustrated in the following table:

	Three Months Ended September 30,
	2018		2017
	(in thousands, except per gallon amounts)				Percent Change
Fuel gallons consumed	109,515		90,274		21.3	%
Into-plane fuel cost per gallon	$	2.36	$	1.75	34.9	%
Into-plane fuel expense	$	258,818	$	158,300	63.5	%
Realized losses (gains) related to fuel derivative contracts, net	—		—		NM
Unrealized losses (gains) related to fuel derivative contracts, net	—		—		NM
Aircraft fuel expense (per statement of operations)	$	258,818	$	158,300	63.5	%

Gulf Coast Jet indexed fuel is the basis for a substantial majority of our fuel consumption and is impacted by both the price of crude oil as well as increases or decreases in refining margins associated with the conversion of crude oil to jet fuel. The into-plane fuel cost per gallon increase of 34.9% was primarily a result of an increase in jet fuel prices.

We track economic fuel expense, which we believe is the best measure of the effect fuel prices are currently having on our business, because it most closely approximates the net cash outflow associated with purchasing fuel used for our operations during the period. We define economic fuel expense as into-plane fuel expense and realized gains or losses on fuel derivative contracts. The key difference between aircraft fuel expense as recorded in our statement of operations and economic fuel expense is unrealized mark-to-market changes in the value of aircraft fuel derivatives outstanding. Many industry analysts evaluate airline results using economic fuel expense and it is used in our internal management reporting.

The elements of the changes in economic fuel expense are illustrated in the following table:

	Three Months Ended September 30,
	2018		2017
	(in thousands, except per gallon amounts)				Percent Change
Into-plane fuel expense	$	258,818	$	158,300	63.5	%
Realized losses (gains) related to fuel derivative contracts, net	—		—		NM
Economic fuel expense	$	258,818	$	158,300	63.5	%
Fuel gallons consumed	109,515		90,274		21.3	%
Economic fuel cost per gallon	$	2.36	$	1.75	34.9	%

During the three months ended September 30, 2018 and 2017, we had no activity related to fuel derivatives and thus had no realized or unrealized losses (gains) related to fuel derivative contracts.

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We measure our operating cost performance on a per-ASM basis, since one ASM is the unit of production of an airline’s capacity. The following table presents our cost per-ASM, or unit cost, for the three months ended September 30, 2018 and 2017, followed by explanations of the material changes on a dollar basis and/or unit cost basis:

	Three Months Ended September 30,					Dollar Change			Percent Change		Cost per ASM			Per-ASM Change		Percent Change
	2018			2017							2018		2017
	(in thousands)										(in cents)
Aircraft fuel	$	258,818		$	158,300	$	100,518		63.5	%	2.70		2.06	0.64		31.1	%
Salaries, wages, and benefits	185,043			134,114		50,929			38.0	%	1.93		1.75	0.18		10.3	%
Aircraft rent	42,682			53,396		(10,714		)	(20.1	)%	0.45		0.70	(0.25	)	(35.7	)%
Landing fees and other rents	54,542			48,498		6,044			12.5	%	0.57		0.63	(0.06	)	(9.5	)%
Depreciation and amortization	43,773			36,840		6,933			18.8	%	0.46		0.48	(0.02	)	(4.2	)%
Maintenance, materials and repairs	37,778			26,176		11,602			44.3	%	0.39		0.34	0.05		14.7	%
Distribution	37,868			29,695		8,173			27.5	%	0.40		0.39	0.01		2.6	%
Special charges (credits)	(686		)	7,853		(8,539		)	NM		(0.01	)	0.10	(0.11	)	NM
Loss on disposal of assets	1,069			516		553			NM		0.01		0.01	—		NM
Other operating	98,318			87,965		10,353			11.8	%	1.03		1.15	(0.12	)	(10.4	)%
Total operating expenses	$	759,205		$	583,353	$	175,852		30.1	%	7.93		7.59	0.34		4.5	%
Adjusted CASM (1)											7.92		7.49	0.43		5.7	%
Adjusted CASM ex-fuel (2)											5.22		5.42	(0.20	)	(3.7	)%

(1) Reconciliation of CASM to Adjusted CASM:

	Three Months Ended September 30,
	2018					2017
	(in millions)			Per ASM		(in millions)		Per ASM
CASM (cents)				7.93				7.59
Unrealized losses (gains) related to fuel derivative contracts, net	$	—		—		$	—	—
Loss on disposal of assets	1.1			0.01		0.5		0.01
Special charges (credits)	(0.7		)	(0.01	)	7.9		0.10
Adjusted CASM (cents)				7.92				7.49

(2) Excludes aircraft fuel expense, loss on disposal of assets and special charges (credits).

Our adjusted CASM ex-fuel for the third quarter of 2018 was down 3.7% as compared to the third quarter of 2017. The decrease on a per-ASM basis was primarily due to decreases in aircraft rent expense and other operating expense.

Labor costs for the third quarter of 2018 increased $50.9 million, or 38.0%, as compared to the third quarter of 2017. The increase was primarily driven by an 18.3% increase in our pilot and flight attendant workforce resulting from an increase to our aircraft fleet of 14 additional aircraft, net of 1 aircraft lease return, since the third quarter of 2017. On a per-ASM basis, labor costs increased due to the rate increase our pilots received in connection with the new collective bargaining agreement that became effective on March 1, 2018.

Aircraft rent expense for the third quarter of 2018 decreased by $10.7 million, or 20.1%, as compared to the third quarter of 2017. This decrease in aircraft rent expense was primarily driven by the purchase of 14 A319 aircraft off lease completed during the second quarter of 2018. For additional information, refer to Note 5, Special Charges. In addition, the return of two leased A321 aircraft in 2017 and higher estimated return costs recorded during the prior period also contributed to the decrease year over year. Costs associated with return conditions of leased aircraft are recorded as supplemental rent within aircraft rent expense on our statement of operations. On a per-ASM basis, aircraft rent expense decreased primarily due to a change in the composition of our aircraft fleet between leased aircraft (for which rent expense is recorded under aircraft rent) and purchased aircraft (for which depreciation expense is recorded under depreciation and amortization). Since the prior year period, we have taken delivery of 15 new purchased aircraft, which increased capacity but had no effect on aircraft rent expense, as these assets were purchased and are being depreciated over their useful life.

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Landing fees and other rents for the third quarter of 2018 increased $6.0 million, or 12.5%, as compared to the third quarter of 2017, primarily due to an 18.3% increase in departures. In addition, landing fees and other rents increased due to an increase in facility rent resulting from the addition of new stations and rate increases at some of our existing stations. On a per-ASM basis, landing fees decreased period over period due to a lower average rate per landing based on the location and volume of where we operated, credits resulting from increased passenger volume and increased signatory adjustments as compared to the prior year period.

Depreciation and amortization for the third quarter of 2018 increased by $6.9 million, or 18.8%, as compared to the prior year period. The increase was primarily due to increased depreciation expense resulting from the purchase of 15 new aircraft made since the third quarter of 2017.

On a per-ASM basis, depreciation and amortization slightly decreased period over period as the increase in depreciation expense was more than offset by a decrease in amortization expense. We account for heavy maintenance under the deferral method. Under the deferral method, the cost of heavy maintenance is capitalized and amortized as a component of depreciation and amortization expense in the statement of operations until the earlier of the next heavy maintenance event or end of the lease term. The amortization of heavy maintenance costs was $8.5 million and $14.2 million for the third quarters of 2018 and 2017, respectively. The decrease, year over year, was primarily due to the timing of maintenance events relative to lease returns for two aircraft returned in the second half of 2017. In addition, amortization expense decreased due to the lengthened amortization period of the heavy maintenance related to 14 aircraft purchased off lease during the second quarter of 2018. Heavy maintenance for these aircraft was previously amortized to the end of the lease term and upon purchase of the respective aircraft, is now amortized to the next maintenance event which resulted in a lengthened amortization period and lower amortization expense as compared to the prior year period. As our fleet continues to grow and age, we expect that the amount of deferred heavy maintenance events will increase and will result in an increase in the amortization of those costs. If heavy maintenance events were amortized within maintenance, materials and repairs expense in the statement of operations, our maintenance, materials and repairs expense would have been $46.3 million and $40.4 million for the third quarter of 2018 and 2017, respectively.

Maintenance, materials and repairs expense for the third quarter of 2018 increased by $11.6 million, or 44.3%, as compared to the third quarter of 2017. The increase in maintenance costs on a dollar basis was due to routine and ongoing maintenance on a growing fleet. On a per-ASM basis, maintenance costs increased as the timing and mix of maintenance events resulted in a greater number of higher cost maintenance events as compared to the prior year period. We expect maintenance expense to increase as our fleet continues to grow and age, resulting in the need for additional or more frequent repairs over time.

Distribution costs increased by $8.2 million, or 27.5%, in the third quarter of 2018 as compared to the third quarter of 2017. The increase on a dollar basis was primarily due to increased sales volume. On a per-ASM basis, distribution costs remained relatively stable year over year.

Other operating expense for the third quarter of 2018 increased by $10.4 million, or 11.8%, as compared to the third quarter of 2017 primarily due to an increase in overall operations. As compared to the prior year period, we increased departures by 18.3% and had 24.6% more passenger flight segments, which drove increases in variable operating expenses. This increase was partially offset by lower passenger re-accommodation expense year over year resulting from better operational performance. This lower passenger re-accommodation expense was the primary driver of the decrease noted in other operating expense on a per-ASM basis, as compared to the prior year period.

Other Income (Expenses)

Our interest expense and corresponding capitalized interest for the three months ended September 30, 2018 and 2017 primarily represents interest related to the financing of purchased aircraft. As of September 30, 2018 and 2017, we had 55 and 40 aircraft financed through secured long-term debt arrangements, respectively. Please see "Notes to Condensed Financial Statements—12. Debt and Other Obligations" for further discussion.

Our interest income for the three months ended September 30, 2018 represents interest income earned on cash, cash equivalents, short-term investments and on funds required to be held in escrow in accordance with the terms of our EETC. Interest income for the three months ended September 30, 2017 primarily represents interest income earned on cash, cash equivalents and short-term investments.

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Income Taxes

Our effective tax rate for the third quarter of 2018 was 24.2% compared to 36.5% for the third quarter of 2017. The decrease in tax rate is attributed to a reduction in the federal statutory tax rate from 35% to 21%, as a result of the enactment of the Tax Cuts and Jobs Act. While we expect our tax rate to be fairly consistent in the near term, it will tend to vary depending on recurring items such as the amount of income we earn in each state and the state tax rate applicable to such income. Discrete items particular to a given year may also affect our effective tax rates.

Comparison of nine months ended September 30, 2018 to nine months ended September 30, 2017

Operating Revenues

Operating revenues increased $482.9 million, or 24.4%, to $2,460.2 million for the nine months ended September 30, 2018, compared to the prior year period, due primarily to an increase in traffic of 25.9%, slightly offset by a decrease in passenger yields of 1.1%.

TRASM for the nine months ended September 30, 2018 was 8.95 cents, a decrease of 1.1% compared to the same period of 2017. This decrease was primarily driven by slightly lower passenger yields, year over year.

Total revenue per passenger flight segment increased slightly from $109.35 for the nine months ended September 30, 2017 to $112.10 for the nine months ended September 30, 2018. Our fare revenue per passenger flight segment increased from $56.74 to $57.36, or 1.1%, as compared to the prior year period, and non-ticket revenue per passenger flight segment increased from $52.61 to $54.74, or 4.0%, as compared to the prior year period. The increase in non-ticket revenue per passenger flight segment was primarily attributable to higher bag revenue, passenger usage fee, and seat revenue per flight segment, as compared to the prior year.

Operating Expenses

Operating expenses increased for the nine months ended September 30, 2018 by $561.5 million, or 33.3%, as compared to the same period for 2017 primarily due to a 25.9% capacity growth and a 25.9% increase in traffic. Furthermore, operating expenses increased as a result of a 31.8% increase in average economic fuel cost per gallon and a 21.9% increase in fuel gallons consumed which drove higher aircraft fuel expense, year over year.

The elements of the changes in aircraft fuel expense are illustrated in the following table:

	Nine Months Ended September 30,
	2018		2017
	(in thousands, except per gallon amounts)				Percent Change
Fuel gallons consumed	310,661		254,871		21.9	%
Into-plane fuel cost per gallon	$	2.28	$	1.73	31.8	%
Into-plane fuel expense	$	709,644	$	440,376	61.1	%
Realized losses (gains) related to fuel derivative contracts, net	—		—		NM
Unrealized losses (gains) related to fuel derivative contracts, net	—		—		NM
Aircraft fuel expense (per Statement of Operations)	$	709,644	$	440,376	61.1	%

The elements of the changes in economic fuel expense are illustrated in the following table:

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	Nine Months Ended September 30,
	2018		2017
	(in thousands, except per gallon amounts)				Percent Change
Into-plane fuel expense	$	709,644	$	440,376	61.1	%
Realized losses (gains) related to fuel derivative contracts, net	—		—		NM
Economic fuel expense	$	709,644	$	440,376	61.1	%
Fuel gallons consumed	310,661		254,871		21.9	%
Economic fuel cost per gallon	$	2.28	$	1.73	31.8	%

During the nine months ended September 30, 2018 and 2017, we had no activity related to fuel derivatives and thus had no realized or unrealized losses (gains) related to fuel derivative contracts.

We measure our operating cost performance on a per-ASM basis, since one ASM is the unit of production of an airline’s capacity. The following table presents our cost per-ASM, or unit cost, for the nine months ended September 30, 2018 and 2017, followed by explanations of the material changes on a unit cost basis and/or dollar basis:

	Nine Months Ended September 30,				Dollar Change			Percent Change		Cost per ASM		Per-ASM Change		Percent Change
	2018		2017							2018	2017
	(in thousands)									(in cents)
Aircraft fuel	$	709,644	$	440,376	$	269,268		61.1	%	2.58	2.02	0.56		27.7	%
Salaries, wages, and benefits	527,895		391,144		136,751			35.0	%	1.92	1.79	0.13		7.3	%
Aircraft rent	134,618		163,032		(28,414		)	(17.4	)%	0.49	0.75	(0.26	)	(34.7	)%
Landing fees and other rents	162,774		134,538		28,236			21.0	%	0.59	0.62	(0.03	)	(4.8	)%
Depreciation and amortization	128,764		103,680		25,084			24.2	%	0.47	0.47	—		—	%
Maintenance, materials and repairs	99,141		81,473		17,668			21.7	%	0.36	0.37	(0.01	)	(2.7	)%
Distribution	103,496		85,302		18,194			21.3	%	0.38	0.39	(0.01	)	(2.6	)%
Special charges (credits)	88,656		12,629		76,027			NM		0.32	0.06	0.26		NM
Loss on disposal of assets	6,561		3,114		3,447			NM		0.02	0.01	0.01		NM
Other operating	283,841		268,553		15,288			5.7	%	1.03	1.23	(0.20	)	(16.3	)%
Total operating expenses	$	2,245,390	$	1,683,841	$	561,549		33.3	%	8.16	7.71	0.45		5.8	%
Adjusted CASM (1)										7.82	7.63	0.19		2.5	%
Adjusted CASM ex-fuel (2)										5.24	5.62	(0.38	)	(6.8	)%

(1) Reconciliation of CASM to Adjusted CASM:

	Nine Months Ended September 30,
	2018			2017
	(in millions)		Per ASM	(in millions)		Per ASM
CASM (cents)			8.16			7.71
Unrealized losses (gains) related to fuel derivative contracts, net	$	—	—	$	—	—
Loss on disposal of assets	6.6		0.02	3.1		0.01
Special charges (credits)	88.7		0.32	12.6		0.06
Adjusted CASM (cents)			7.82			7.63

(2) Excludes aircraft fuel expense, loss on disposal of assets and special charges and credits.

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Our adjusted CASM ex-fuel for the nine months ended September 30, 2018 decreased by 6.8% as compared to the same period in 2017. The decrease on a per-ASM basis was primarily due to decreases in aircraft rent expense and other operating expense.

Labor costs for the nine months ended September 30, 2018 increased $136.8 million, or 35.0%, as compared to the same period in 2017. The increase was primarily driven by a 22.1% increase in our pilot and flight attendant workforce resulting from an increase to our aircraft fleet of 14 additional aircraft, net of 1 aircraft lease return, since the end of the third quarter of 2017. On a per-ASM basis, labor costs increased due to the rate increase our pilots received in connection with the new collective bargaining agreement that became effective on March 1, 2018.

Aircraft rent expense for the nine months ended September 30, 2018 decreased by $28.4 million, or 17.4%, as compared to the same period in 2017. This decrease in aircraft rent expense was primarily driven by the purchase of 14 A319 aircraft off lease completed during the second quarter of 2018. For additional information, refer to Note 5, Special Charges. In addition, the return of two leased A321 aircraft in 2017 and higher estimated return costs recorded during the prior period also contributed to the decrease year over year. Costs associated with return conditions of leased aircraft are recorded as supplemental rent within aircraft rent expense on our statement of operations. On a per-ASM basis, aircraft rent expense decreased primarily due to a change in the composition of our aircraft fleet between leased aircraft (for which rent expense is recorded under aircraft rent) and purchased aircraft (for which depreciation expense is recorded under depreciation and amortization). Since the prior year period, we have purchased 15 new aircraft, which increased capacity but had no effect on aircraft rent expense, as these assets were purchased and are being depreciated over their useful life.

Landing fees and other rents for the nine months ended September 30, 2018 increased $28.2 million, or 21.0%, as compared to the same period in 2017 primarily due to a 17.2% increase in departures. In addition, landing fees and other rents increased due to an increase in facility rent resulting from the addition of new stations and rate increases at some of our existing stations. On a per-ASM basis, landing fees decreased slightly period over period due to a lower average rate per landing based on the location and volume of where we operated, credits resulting from increased passenger volume and increased signatory adjustments as compared to the prior year period.

Depreciation and amortization increased by $25.1 million, or 24.2%, as compared to the prior year period. The increase was primarily due to increased depreciation expense resulting from the purchase of 15 new aircraft made since the third quarter of 2017.

On a per-ASM basis, depreciation and amortization expense remained stable as the increase in depreciation expense was offset by a decrease in amortization expense.We account for heavy maintenance under the deferral method. Under the deferral method, the cost of heavy maintenance is capitalized and amortized as a component of depreciation and amortization expense in the statement of operations until the earlier of the next heavy maintenance event or end of the lease term. The amortization of heavy maintenance costs was $29.9 million and $42.1 million for the nine months ended September 30, 2018 and 2017, respectively. The decrease, year over year, was primarily due to the timing of maintenance events relative to lease returns for two aircraft returned in the second half of 2017. In addition, amortization expense decreased due to the lengthened amortization period of the heavy maintenance related to 14 aircraft purchased off lease during the second quarter of 2018. Heavy maintenance for these aircraft was previously amortized to the end of the lease term and upon purchase of the respective aircraft, is now amortized to the next maintenance event which resulted in a lengthened amortization period and lower amortization expense as compared to the prior year period. As our fleet continues to age, we expect that the amount of deferred heavy maintenance events will increase and will result in an increase in the amortization of those costs. If heavy maintenance events were amortized within maintenance, materials and repairs expense in the statement of operations, our maintenance, materials and repairs expense would have been $129.1 million and $123.5 million for the nine months ended September 30, 2018 and 2017, respectively.

Maintenance, materials and repairs expense for the nine months ended September 30, 2018 increased by $17.7 million, or 21.7%, as compared to the prior year period. The increase in maintenance costs on a dollar basis was due to routine and ongoing maintenance on a growing fleet. The timing and mix of maintenance events resulted in relatively stable maintenance costs on a per-ASM basis year over year. We expect maintenance expense to increase as our fleet continues to grow and age, resulting in the need for additional or more frequent repairs over time.

Distribution costs increased by $18.2 million, or 21.3%, for the nine months ended September 30, 2018 as compared to the same period in 2017. The increase on a dollar basis was primarily due to increased sales volume. On a per-ASM basis, distribution costs remained relatively stable, as compared to the prior period.

Other operating expense for the nine months ended September 30, 2018 increased by $15.3 million, or 5.7%, as compared to the prior period, primarily due to an increase in overall operations. As compared to the prior year period, we increased departures by 17.2% and had 21.4% more passenger flight segments, which drove increases in variable operating expenses.

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Improved operational performance, year over year, resulted in lower passenger reaccommodation expense which partially offset the increase noted on a dollar basis. Lower passenger reaccommodation expense also contributed to a decrease in other operating expense on a per-ASM basis.

Special charges for the nine months ended September 30, 2018 consisted of $88.7 million recognized in connection with the new pilot agreement approved in February 2018. The total amount includes a one-time $80.2 million ratification incentive, including payroll taxes, and an $8.5 million adjustment related to other contractual provisions. For the nine months ended September 30, 2017, special charges consisted of $12.6 million in lease termination charges recognized in connection with the purchase of 1 aircraft and 1 engine, which were formerly financed under operating lease agreements. The amount recorded as lease termination charges represents the excess of the purchase price paid over the appraised fair value of the asset(s), less previously expensed supplemental rent and other non-cash items. For additional information, please refer to "Notes to Condensed Financial Statements - 5. Special Charges."

Other income (expenses)

Our interest expense and corresponding capitalized interest for the nine months ended September 30, 2018 and 2017 primarily represents interest related to the financing of purchased aircraft. As of September 30, 2018 and 2017, the Company had 55 and 40 aircraft financed through secured long-term debt arrangements, respectively. Please see "Notes to Condensed Financial Statements—12. Debt and Other Obligations" for further discussion.

Our interest income for the nine months ended September 30, 2018 represents interest income earned on cash, cash equivalents, short-term investments and on funds required to be held in escrow in accordance with the terms of our EETC. Interest income for the nine months ended September 30, 2017 primarily represents interest income earned on cash, cash equivalents and short-term investments.

Our special charges, non-operating for the nine months ended September 30, 2018, represents interest related to the aircraft purchase agreement for the acquisition of 14 A319 aircraft previously operated under operating leases. The contract was deemed a lease modification which resulted in a change of classification from operating leases to capital leases. Please see "Notes to Condensed Financial Statements—5. Special Charges" for further discussion.

Income Taxes

Our effective tax rate for the nine months ended September 30, 2018 was 24.1% compared to 37.1% for the nine months ended September 30, 2017. The decrease in tax rate is attributed to a reduction in the federal statutory tax rate from 35% to 21%, as a result of the enactment of the Tax Cuts and Jobs Act. While we expect our tax rate to be fairly consistent in the near term, it will tend to vary depending on recurring items such as the amount of income we earn in each state and the state tax rate applicable to such income. Discrete items particular to a given year may also affect our effective tax rates.

Liquidity and Capital Resources

Our primary sources of liquidity are cash on hand, cash provided by operations and capital from debt financing. Primary uses of liquidity are for working capital needs, capital expenditures, aircraft and engine pre-delivery deposit payments ("PDPs"), debt obligations and maintenance reserves. Our total cash at September 30, 2018 was $773.7 million, a decrease of $27.1 million from December 31, 2017. In addition to cash and cash equivalents, as of September 30, 2018, we had $102.2 million in short-term investment securities.

Currently, one of our largest capital expenditure needs is funding the acquisition costs of our aircraft. Aircraft may be acquired through debt financing, cash purchases, direct leases or sale leaseback transactions. During the nine months ended September 30, 2018, we purchased 9 aircraft through debt financing transactions and made $144.8 million in debt payments (principal, interest and fees) on our outstanding debt obligations. The debt entered into in the current year has maturity dates ranging from 2023 to 2030 and interest rates ranging from 3.375% to 5.110%. In addition, during the nine months ended September 30, 2018, we purchased eight engines through cash purchases and sold five engines.

Under our agreement with Airbus for aircraft, and International Aero Engines AG ("IAE") and Pratt & Whitney for engines, we are required to pay PDPs relating to future deliveries at various times prior to each delivery date. During the nine months ended September 30, 2018, we paid $132.3 million in PDPs, net of refunds, and $6.1 million of capitalized interest for future deliveries of aircraft and spare engines. As of September 30, 2018, we had $253.8 million of PDPs, including capitalized interest, on our balance sheet.

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On October 23, 2018, we entered into a revolving credit facility for up to $160 million secured by the collateral assignment of certain of our rights under our purchase agreement with Airbus, related to 43 Airbus A320neo aircraft scheduled to be delivered between August 2019 and December 2021. We intend to use any proceeds for working capital, capital expenditures and other general corporate purposes. The final maturity of the facility is December 30, 2020. As of October 24, 2018, no amounts have been drawn.

As of September 30, 2018, we had secured debt financing for one aircraft, delivered in October 2018. In addition, we secured financing for seven aircraft to be leased directly from a third-party lessor, scheduled for delivery in 2018 through 2019. Aircraft rent commitments for these 7 leased aircraft are expected to be approximately $1.0 million for the remainder of 2018, $27.2 million in 2019, $29.4 million in 2020, $29.4 million in 2021, $29.4 million in 2022, and $235.9 million in 2023 and beyond. As of September 30, 2018, we do not have financing commitments in place for the remaining 49 Airbus firm aircraft orders, scheduled for delivery between 2018 through 2021. Future aircraft deliveries may be paid in cash, leased or otherwise financed based on market conditions, our prevailing level of liquidity, and capital market availability. During the first quarter of 2018, we entered into an aircraft purchase agreement for the purchase of 14 A319s, which were previously financed under operating lease agreements. The contract was deemed a lease modification which resulted in a change of classification from operating leases to capital leases for the 14 aircraft. The purchase of all 14 aircraft was completed during the second quarter of 2018, for an aggregate purchase price of $285.0 million, which was comprised of cash payments, net of the application of cash maintenance and security deposits held by the previous lessor. For additional information, refer to "Notes to Condensed Financial Statements - 5. Special Charges."

In addition to funding the acquisition of our future fleet, we are required to make maintenance reserve payments for some of the aircraft in our current fleet. Maintenance reserves are paid to aircraft lessors and are held as collateral in advance of our performance of major maintenance activities. During the nine months ended September 30, 2018, we recorded an increase of $10.5 million in maintenance reserves, net of reimbursements, and as of September 30, 2018, we had $249.1 million ($104.5 million in aircraft maintenance deposits and $144.6 million in long-term aircraft maintenance deposits) on our condensed balance sheet.

On October 25, 2017, our Board of Directors authorized a repurchase program of up to $100 million in aggregate value of shares of our Common Stock, par value $0.0001 per share, from time to time in open market or privately negotiated transactions. The authorization will expire on October 25, 2018. The timing and amount of any stock repurchases are subject to prevailing market conditions and other considerations. As of September 30, 2018, we had repurchased 1.2 million shares for $44.9 million under our stock repurchase program.

Net Cash Flows Provided By Operating Activities. Operating activities in the nine months ended September 30, 2018 provided $308.5 million in cash compared to $387.3 million provided in the nine months ended September 30, 2017. The decrease is primarily due to special charges within operating income recorded for the nine months ended September 30, 2018 associated with the amended pilot agreement, approved in February 2018. For additional information, refer to "Notes to Condensed Financial Statements - 5. Special Charges." In addition, we had a decrease in deferred income tax expense and deferred heavy maintenance, year over year. These decreases were partially offset by increases in special charges, non-operating and other liabilities.

Net Cash Flows Used In Investing Activities. In the nine months ended September 30, 2018, investing activities used $550.6 million, compared to $559.6 million used in the prior year period. The decrease was mainly driven by fewer purchases of property and equipment, year over year, as well as increased proceeds received from the sale of property and equipment.

Net Cash Flows Provided By Financing Activities. During the nine months ended September 30, 2018, financing activities provided $215.0 million in cash compared to $335.1 million provided in the nine months ended September 30, 2017. We received $518.2 million in connection with the 2015-1C and 2017-1C EETCs and the debt financing related to nine aircraft delivered during the nine months ended September 30, 2018. In addition, we paid $93.2 million in debt obligations and $205.6 million in capital lease obligations. The payments on capital lease obligations are primarily related to an aircraft purchase agreement for the purchase of 14 A319 aircraft which were previously operated by the Company under operating leases. For additional information, refer to "Notes to Condensed Financial Statements - 5. Special Charges."

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Commitments and Contractual Obligations

We have contractual obligations and commitments primarily with regard to future purchases of aircraft and engines, payment of debt, and lease arrangements. The following table discloses aggregate information about our contractual obligations as of September 30, 2018 and the periods in which payments are due (in millions): 

	remainder of 2018		2019 - 2020		2021 - 2022		2023 and beyond		Total
Long-term debt (1)	$	44	$	314	$	299	$	1,308	$	1,965
Interest commitments (2)	22		146		120		179		467
Capital and operating lease obligations	58		405		338		522		1,323
Flight equipment purchase obligations	210		1,403		792		8		2,413
Other (3)	3		25		20		67		115
Total future payments on contractual obligations	$	337	$	2,293	$	1,569	$	2,084	$	6,283

(1) Includes principal only associated with senior and junior term loans, Class A, Class B, and Class C Series 2015-1 EETCs, and Class AA, Class A, Class B, and Class C Series 2017-1 EETCs. Refer to "Notes to the Financial Statements - 12. Debt and Other Obligations."

(2) Related to senior and junior term loans, fixed-rate loans, and Class A, Class B, and Class C Series 2015-1 EETCs, and Class AA, Class A, Class B, and Class C Series 2017-1 EETCs.

(3) Primarily related to our reservation system and other miscellaneous subscriptions and services. Refer to "Notes to the Financial Statements - 10. Commitments and Contingencies."

Some of our master lease agreements provide that we pay maintenance reserves to aircraft lessors to be held as collateral in advance of our required performance of major maintenance activities. Some maintenance reserve payments are fixed contractual amounts, while others are based on utilization. In addition to the contractual obligations disclosed in the table above, we have fixed maintenance reserve payments for these aircraft and related flight equipment, including estimated amounts for contractual price escalations, which are $1.8 million for the remainder of 2018, $5.8 million in 2019, $5.6 million in 2020, $5.7 million in 2021, $4.9 million in 2022, and $12.9 million in 2023 and beyond.

As of September 30, 2018, principal and interest commitments related to our future secured debt financing for 1 undelivered aircraft to be financed under the Series 2017-1 EETC are $0 for the remainder of 2018, $4.4 million in 2019, $4.0 million in 2020, $3.3 million in 2021, $3.1 million in 2022, and $34.0 million in 2023 and beyond.

Off-Balance Sheet Arrangements

We have significant obligations for aircraft and spare engines as 44 of our 121 aircraft and 12 of our 18 spare engines are financed under operating leases and therefore are not reflected on our balance sheets. These leases expire between 2019 and 2031. Aircraft rent payments were $44.3 million and $55.0 million for the three months ended September 30, 2018 and 2017, respectively, and $170.8 million and $168.6 million for the nine months ended September 30, 2018 and 2017, respectively. Our aircraft lease payments for 43 of our aircraft are fixed-rate obligations. One of our leases provide for variable rent payments, which fluctuate based on changes in LIBOR.

Our contractual purchase commitments consist primarily of aircraft and engine acquisitions through manufacturers. During the first quarter of 2018, we negotiated revisions to our A320 aircraft order. We originally had 14 A320neo aircraft scheduled for delivery in 2019. Pursuant to the revisions, 5 of the 14 scheduled A320neo aircraft were converted to A320ceo aircraft and are scheduled to be delivered in the remainder of 2018 and 2019. During the third quarter of 2018, we entered into operating lease agreements for the lease of seven A320neos that are scheduled to be delivered in the remainder of 2018 and 2019. As of September 30, 2018, our firm aircraft orders consisted of the following:

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	Airbus		Third-Party Lessor
	A320ceo	A320neo	A320neo	Total
remainder of 2018	5		3	8
2019	2	9	4	15
2020		16		16
2021		18		18
	7	43	7	57

During the first quarter of 2018, we entered into an aircraft purchase agreement for the purchase of 14 A319 aircraft, which were previously financed under operating lease agreements. The contract was deemed a lease modification which resulted in a change of classification from operating leases to capital leases for the 14 aircraft. As a result, we recorded a short-term capital lease asset of $236.7 million within flight equipment and a short-term capital lease obligation of $143.8 million, net of the related maintenance and security deposits, within current maturities of long-term debt and capital leases on the condensed balance sheet as of March 31, 2018. The purchase of all 14 aircraft was completed during the second quarter of 2018 for an aggregate gross purchase price of $285.0 million, which was comprised of cash payments, net of the application of cash maintenance and security deposits held by the previous lessor. For additional information, refer to "Notes to Condensed Financial Statements - 5. Special Charges."

During the first quarter of 2018, we entered into an agreement to purchase six new engines. As of September 30, 2018, we had purchased all six engines, unencumbered. We also have two spare engine orders for V2500 SelectTwo engines with IAE and nine spare engine orders for PurePower PW 1100G-JM engines with Pratt & Whitney. Spare engines are scheduled for delivery from 2018 through 2023. Committed expenditures for these aircraft and spare engines, including estimated amounts for contractual price escalations and aircraft PDPs, are expected to be $210.2 million for the remainder of 2018, $592.1 million in 2019, $810.8 million in 2020, $775.4 million in 2021, $17.0 million in 2022 and $8.0 million in 2023 and beyond.

As of September 30, 2018, we had lines of credit related to corporate credit cards of $33.6 million from which we had drawn $10.1 million.

As of September 30, 2018, we had lines of credit with counterparties for both physical fuel delivery and derivatives in the amount of $51.5 million. As of September 30, 2018, we had drawn $19.7 million on these lines of credit for physical fuel delivery. We are required to post collateral for any excess above the lines of credit if the derivatives are in a net liability position and make periodic payments in order to maintain an adequate undrawn portion for physical fuel delivery. As of September 30, 2018, we did not hold any derivatives.

As of September 30, 2018, we have $9.4 million in uncollateralized surety bonds and a $35.0 million unsecured standby letter of credit facility, representing an off balance-sheet commitment, of which $17.3 million had been drawn upon for issued letters of credit.

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GLOSSARY OF AIRLINE TERMS

Set forth below is a glossary of industry terms:

“Adjusted CASM” means operating expenses, excluding unrealized gains or losses related to fuel derivative contracts, out of period fuel federal excise tax, loss on disposal of assets, special charges (credits) and supplemental rent adjustment for liabilities accrued in prior years that are no longer probable, divided by ASMs.

“Adjusted CASM ex-fuel” means operating expenses excluding aircraft fuel expense, loss on disposal of assets, special charges (credits) and supplemental rent adjustment for liabilities accrued in prior years that are no longer probable, divided by ASMs.

“AFA-CWA” means the Association of Flight Attendants-CWA.

“Air traffic liability” or “ATL” means the value of tickets sold in advance of travel.

“ALPA” means the Air Line Pilots Association, International.

“ASIF” means an Aviation Security Infrastructure Fee assessed by the TSA on each airline.

“Available seat miles” or “ASMs” means the number of seats available for passengers multiplied by the number of miles the seats are flown, also referred to as "capacity."

“Average aircraft” means the average number of aircraft in our fleet as calculated on a daily basis.

“Average daily aircraft utilization” means block hours divided by number of days in the period divided by average aircraft.

“Average economic fuel cost per gallon” means total aircraft fuel expense, excluding unrealized gains or losses related to fuel derivative contracts and out of period fuel federal excise tax, divided by the total number of fuel gallons consumed.

“Average stage length” represents the average number of miles flown per flight.

“Average yield” means average operating revenue earned per RPM, calculated as total revenue divided by RPMs, also referred to as "passenger yield."

“Block hours” means the number of hours during which the aircraft is in revenue service, measured from the time of gate departure before take-off until the time of gate arrival at the destination.

“CASM” or “unit costs” means operating expenses divided by ASMs.

“CBA” means a collective bargaining agreement.

“CBP” means United States Customs and Border Protection.

“DOT” means the United States Department of Transportation.

“EPA” means the United States Environmental Protection Agency.

"EETC" means enhanced equipment trust certificate.

“FAA” means the United States Federal Aviation Administration.

“Fare revenue per passenger flight segment” means total fare passenger revenue divided by passenger flight segments.

“FCC” means the United States Federal Communications Commission.

"FLL Airport" means the Fort Lauderdale Hollywood International Airport.

“GDS” means Global Distribution System (e.g., Amadeus, Galileo, Sabre and Worldspan).

"IAMAW" means the International Association of Machinists and Aerospace Workers.

“Into-plane fuel cost per gallon” means into-plane fuel expense divided by number of fuel gallons consumed.

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“Into-plane fuel expense” represents the cost of jet fuel and certain other charges such as fuel taxes and oil.

“Load factor” means the percentage of aircraft seats actually occupied on a flight (RPMs divided by ASMs).

"Non-ticket revenue" means the sum of non-fare passenger revenues and other revenues.

“Non-ticket revenue per passenger flight segment” means total non-fare passenger revenue and other revenue divided by passenger flight segments.

“NMB” means the National Mediation Board.

“OTA” means Online Travel Agent (e.g., Orbitz and Travelocity).

“Passenger flight segments” means the total number of passengers flown on all flight segments.

“PDP” means pre-delivery deposit payment.

"PAFCA" means the Professional Airline Flight Control Association.

“Revenue passenger mile” or “RPM” means one revenue passenger transported one mile. RPMs equals revenue passengers multiplied by miles flown, also referred to as “traffic.”

“RLA” means the United States Railway Labor Act.

"Total operating revenue per-ASM," "TRASM" or "unit revenue" means operating revenue divided by ASMs.

“TWU” means the Transport Workers Union of America.

“TSA” means the United States Transportation Security Administration.

“ULCC” means “ultra low-cost carrier.”

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ITEM 3. QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK

Market Risk-Sensitive Instruments and Positions

We are subject to certain market risks, including commodity prices (specifically aircraft fuel) and interest rates. We purchase the majority of our jet fuel at prevailing market prices and seek to manage market risk through execution of our hedging strategy and other means. We have market-sensitive instruments in the form of fixed-rate debt instruments, short-term investment securities and, from time to time, financial derivative instruments used to hedge our exposure to jet fuel price increases and interest rate increases. We do not purchase or hold any derivative financial instruments for trading purposes. The adverse effects of changes in these markets could pose a potential loss as discussed below. The sensitivity analysis provided below does not consider the effects that such adverse changes may have on overall economic activity, nor does it consider additional actions we may take to mitigate our exposure to such changes. Actual results may differ.

Aircraft Fuel. Our results of operations can vary materially due to changes in the price and availability of aircraft fuel. Aircraft fuel expense for the nine months ended September 30, 2018 and 2017 represented approximately 31.6% and 26.2% of our operating expenses, respectively. Volatility in aircraft fuel prices or a shortage of supply could have a material adverse effect on our operations and operating results. We source a significant portion of our fuel from refining resources located in the southeast United States, particularly facilities adjacent to the Gulf of Mexico. Gulf Coast fuel is subject to volatility and supply disruptions, particularly during hurricane season when refinery shutdowns have occurred, or when the threat of weather related disruptions has caused Gulf Coast fuel prices to spike above other regional sources. Both jet fuel swaps and jet fuel options are used at times to protect the refining price risk between the price of crude oil and the price of refined jet fuel, and to manage the risk of increasing fuel prices. Gulf Coast Jet indexed fuel is the basis for a substantial majority of our fuel consumption. Based on our annual fuel consumption over the last twelve months, a hypothetical 10% increase in the average price per gallon of aircraft fuel would have increased into-plane aircraft fuel expense by approximately $88 million.

As of September 30, 2018 and December 31, 2017, we did not have any outstanding jet fuel derivatives. We measure our financial derivative instruments at fair value. Fair value of the instruments is determined using standard option valuation models. Changes in the related commodity derivative instrument cash flows may change by more or less than the amount based upon further fluctuations in future prices. Outstanding financial derivative instruments expose us to credit loss in the event of nonperformance by the counterparties to the agreements. However, we do not expect the counterparties to fail to meet their obligations.

Interest Rates. We have market risk associated with our short-term investment securities, which had a fair market value of $102.2 million and $100.9 million, as of September 30, 2018 and December 31, 2017, respectively. We also have market risk associated with changing interest rates due to LIBOR-based lease rates on one of our aircraft. A hypothetical 10% change in interest rates would affect total aircraft rent expense by less than $0.1 million per annum.

Fixed-Rate Debt. As of September 30, 2018, we had $1,964.6 million outstanding in fixed-rate debt related to the purchase of 25 Airbus A320 aircraft and 30 Airbus A321 aircraft which had a fair value of $1,940.3 million. As of December 31, 2017, we had $1,539.6 million outstanding in fixed-rate debt related to the purchase of 21 Airbus A320 aircraft and 25 Airbus A321 aircraft, which had a fair value of $1,583.2 million.

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ITEM 4. CONTROLS AND PROCEDURES

Evaluation of Disclosure Controls and Procedures

Management, with the participation of our Chief Executive Officer and our Chief Financial Officer, evaluated the effectiveness of our disclosure controls and procedures as of September 30, 2018. The term “disclosure controls and procedures,” as defined in Rules 13a-15(e) and 15d-15(e) under the Exchange Act, means controls and other procedures of a company that are designed to ensure that information required to be disclosed by a company in the reports that it files or submits under the Exchange Act is recorded, processed, summarized and reported, within the time periods specified in the SEC’s rules and forms. Disclosure controls and procedures include, without limitation, controls and procedures designed to ensure that information required to be disclosed by a company in the reports that it files or submits under the Exchange Act is accumulated and communicated to the our management, including its principal executive and principal financial officers, as appropriate to allow timely decisions regarding required disclosure.

Management recognizes that any controls and procedures, no matter how well designed and operated, can provide only reasonable assurance of achieving their objectives and management necessarily applies its judgment in evaluating the cost-benefit relationship of possible controls and procedures. Based on the evaluation of our disclosure controls and procedures as of September 30, 2018, our Chief Executive Officer and Chief Financial Officer concluded that, as of such date, our disclosure controls and procedures were effective at the reasonable assurance level.

Changes in Internal Control over Financial Reporting

There were no changes in our internal control over financial reporting (as defined in Rule 13a-15(f) under the Exchange Act) during the quarter ended September 30, 2018, that have materially affected, or are reasonably likely to materially affect, our internal control over financial reporting.

46

PART II. OTHER INFORMATION

ITEM 1. LEGAL PROCEEDINGS

We are subject to commercial litigation claims and to administrative and regulatory proceedings and reviews that may be asserted or maintained from time to time. We believe the ultimate outcome of such lawsuits, proceedings and reviews will not, individually or in the aggregate, have a material adverse effect on our financial position, liquidity or results of operations.

47

ITEM 1A. RISK FACTORS

There have been no material changes to the risk factors disclosed in Item 1A Risk Factors contained in our Annual Report on Form 10-K for the year ended December 31, 2017, filed with the Securities and Exchange Commission on February 13, 2018, other than as disclosed in Part II, Item 1A. Risk Factors contained in our Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2018, filed with the Securities and Exchange Commission on April 26, 2018. Investors are urged to review these risk factors carefully.

48

ITEM 2. UNREGISTERED SALES OF EQUITY SECURITIES AND USE OF PROCEEDS

Repurchases of Equity Securities

The following table reflects our repurchases of our common stock during the third quarter of 2018. All stock repurchases during this period were made from employees who received restricted stock awards. All employee stock repurchases were made at the election of each employee pursuant to an offer to repurchase by us. In each case, the shares repurchased constituted the portion of vested shares necessary to satisfy tax withholding requirements.

ISSUER PURCHASES OF EQUITY SECURITIES
Period	Total Number of Shares Purchased	Average Price Paid per Share		Total Number of Shares Purchased as Part of Publicly Announced Plans or Programs	Approximate Dollar Value of Shares that May Yet be Purchased Under Plans or Programs
July 1-31, 2018	—	$	—	—	$	55,076,306
August 1-31, 2018	861	$	43.86	—	$	55,076,306
September 1-30, 2018	2,655	$	45.55	—	$	55,076,306
Total	3,516	$	45.13	—

On October 25, 2017, our Board of Directors authorized a new repurchase program of up to $100 million in aggregate value of shares of our Common Stock, par value $0.0001 per share, from time to time in open market or privately negotiated transactions. The authorization will expire on October 25, 2018. The timing and amount of any stock repurchases are subject to prevailing market conditions and other considerations. As of September 30, 2018, 1.2 million shares had been repurchased under this stock repurchase program for $44.9 million.

ITEM 3. DEFAULTS UPON SENIOR SECURITIES

None

ITEM 4. MINE SAFETY DISCLOSURES

Not applicable

ITEM 5. OTHER INFORMATION

None

49

ITEM 6. EXHIBITS

Exhibit Number	Description of Exhibits
10.1	Rocky B. Wiggins Offer Letter.
10.2	Scott M. Haralson Offer Letter.
31.1	Certification of the Chief Executive Officer pursuant to Section 302 of the Sarbanes-Oxley Act of 2002.
31.2	Certification of the Chief Financial Officer pursuant to Section 302 of the Sarbanes-Oxley Act of 2002.
32.1*	Certification of the Chief Executive Officer pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002.
32.2*	Certification of the Chief Financial Officer pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002.
101.INS	XBRL Instance Document - The instance document does not appear in the interactive data file because its XBRL tags are embedded within the inline XBRL document.
101.SCH	XBRL Taxonomy Extension Schema
101.CAL	XBRL Taxonomy Extension Calculation Linkbase
101.LAB	XBRL Taxonomy Extension Label Linkbase
101.PRE	XBRL Taxonomy Extension Presentation Linkbase

* Exhibits 32.1 and 32.2 are being furnished and shall not be deemed to be “filed” for purposes of Section 18 of the Exchange Act, or otherwise subject to the liability of that section, nor shall such exhibits be deemed to be incorporated by reference in any registration statement or other document filed under the Securities Act or the Exchange Act, except as otherwise specifically stated in such filing.

50

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.

	SPIRIT AIRLINES, INC.
Date: October 24, 2018	By:	/s/ Scott M. Haralson
		Scott M. Haralson
		Senior Vice President and Chief Financial Officer

51

EX-10.1

Exhibit 10.1    

July 25, 2016

Rocky B. Wiggins

##############

##############

Dear Rocky,

On behalf of Spirit Airlines, Inc. (“Spirit” or the “Company”), I would like to take this opportunity to confirm the terms of our offer of employment. We are enthusiastic about you joining the Spirit Team!

1.    Your title will be Senior Vice President & Chief Information Officer, and you will report directly to the President & Chief Executive Officer.

2.    Your annualized base salary will be $335,000, which results in a semi-monthly payroll amount of $13,958.34 (gross – subject to withholdings for taxes and appropriate deductions). Your base salary will be subject to annual review in accordance with the Company’s executive compensation program and practices.

3.    You will be eligible to participate in the Company’s Short-Term Incentive Plan (STI) for Officers at the Senior Vice President (SVP) level assuming that you are in active employment status prior to October 1, 2016. Your STI target will be 70% of base salary earnings paid during the STI plan year. For the 2016 STI plan year, you will be eligible for a pro-rated STI payment based on the time you are employed at the Company during the 2016 STI plan year. Your actual STI payment can range from 0% to 200% of target depending on (i) the Company’s safety performance during the year, (ii) the Company’s performance under applicable financial and operational metrics and (iii) to the extent applicable, our Compensation Committee’s assessment of your individual performance. STI bonuses earned for any year are usually paid during the first calendar quarter of the following year and are subject to the approval and discretion of the Compensation Committee of the Board of Directors. In no event will you be entitled to receive an STI payment for any year unless your employment with the Company continued through the last day of that year and you are actively on the payroll of Spirit Airlines on the date of the STI payment.

4.    Subject to approval by our Compensation Committee, you will be granted an initial off-cycle equity-based incentive award (the “Off-Cycle LTI Award”) having a grant face value of $900,000 (based on the average closing price of Spirit common stock for the 5 trading days prior to the date of grant). The Off-Cycle LTI Award will be subject to the terms and conditions of the Company’s 2015 Incentive Award Plan, as amended from time to time (“Incentive Award Plan”). The Off-Cycle LTI Award will be in the form of Restricted Stock Units, vesting over a four-year period as follows: 50% on the second anniversary of the grant date, 25% on the third anniversary of the grant date and the remaining 25% on the fourth anniversary of the grant date. Should your employment with the Company terminate for any reason (other than death or permanent disability), prior to the fourth anniversary of the grant date, the unvested portion of the Off-Cycle LTI Award would automatically terminate and forfeit at that time. It is contemplated that the grant of the Off-Cycle LTI Award would be approved by our Compensation Committee at its first meeting following your start date. The next meeting of the Compensation Committee is scheduled for August 15, 2016.

1

Exhibit 10.1    

5.    Commencing in 2017, during your employment with the Company, you will be eligible to be granted annual long-term incentive equity awards (“Annual LTI Awards”) under the Incentive Award Plan. Your eligibility to receive an Annual LTI Award in any year will be on the basis, terms and conditions determined by the Compensation Committee in its discretion. It is contemplated that the 2017 Annual LTI Awards at the SVP level will have a grant date value of $450,000 and will be split 50/50 between Restricted Stock Units, vesting in equal annual installments over a four-year period, and Performance Share Units, to be settled in shares of Company common stock after a three-year measurement period. Your Annual LTI Awards will be granted at the same time Annual LTI Awards are granted to other senior executive officers. Should your employment with the Company terminate for any reason (other than death or permanent disability) prior to the vesting date of any Annual LTI Award granted to you, the unvested portion of such Annual LTI Award will automatically terminate and forfeit at that time.

6.    You will be entitled to a signing bonus of $175,000 (gross – subject to withholdings for taxes and applicable deductions) payable in cash within thirty days after your start date. Should you terminate your employment with the Company at any time within 12 months following your start date, you hereby agree to promptly repay the full signing bonus to the Company.

7.    To assist with your relocation to South Florida, the Company is prepared to reimburse you for up to $100,000 (gross - subject to withholding for taxes and other required deductions) in relocation expenses that are documented in reasonable detail. You hereby agree to promptly repay to the Company, in full, all amounts paid or reimbursed to you by the Company for relocation if you terminate employment with the Company at any time within 12 months following your start date.

8.    Commencing ninety days from your start date, you will be eligible to participate in Company sponsored employee benefits, including medical, life, dental, vision insurance and the voluntary benefit plans. You will be eligible for the Company’s 401(k) plan participation after sixty days of employment. You must complete all enrollment forms within your first ninety days. On your start date, you and your immediate family will be eligible for positive space airline travel privileges on Spirit, and after six months, you will be eligible to receive Spirit buddy passes according to the Company’s program. You will also receive travel privileges on other specified airlines subject to their policies and their respective agreements with the Company. Your eligibility for the foregoing benefits will automatically terminate if you cease to be employed by the Company for any reason. Of course, the Company may change its benefits package at any time.

9.    You agree that the Company may withhold from any compensation, reimbursements and benefits payable to you all taxes as required by law and well as other standard or customary withholdings and deductions. You also agree that target incentives do not constitute a promise of payment.

10.    Under the Company’s current vacation pay policy, on your start date, you will begin to accrue vacation at a semi-monthly rate of 5.00 hours per pay period. If you worked an entire year, you would be eligible to accrue a maximum of three weeks. Of course, the Company may change or discontinue the policy at any time.

11.    As an officer of the Company, you will be eligible for participation in the Spirit Airlines, Inc. Executive Severance Plan (as amended), a copy of which will be provided to you under separate cover. In addition, as an officer of the Company, you will be covered by the Company's directors and officers’ liability insurance policy, which may be changed or discontinued by the Company at any time.

12.    Please note and understand that, consistent with Company practice, your employment with the Company constitutes “at will” employment and will not be for a specified period. As a result, your employment with the Company may be terminated by you or the Company at any time, with or without cause and with or without advance notice.

2

Exhibit 10.1    

13.    As an employee of the Company, you will be expected and required to abide by the Company’s policies and procedures, including (but not limited to) the Company’s Code of Business Conduct and Ethics and Insider Trading Compliance Program.

14.    This offer is contingent upon your passing required Company and TSA background checks, as well as you signing and returning this letter to us no later than July 28, 2016, and commencing employment on or prior to September 1, 2016 or a date mutually agreeable. Our Human Resources Department will be in touch with you to coordinate pre-employment arrangements.

15.    You agree and warrant that in performing services for the Company, you will not use or disclose any confidential information of any prior employer or other person or entity. You further warrant and represent that you have not taken or brought with you any confidential, proprietary or potentially trade secret information from any prior employer or other person or entity for use at the Company, and that you are able to fully and effectively perform your job functions for the Company without resort to, or reliance on, any such confidential information of any prior employer or other person or entity. You further warrant and represent that your acceptance of this offer and your employment with the Company will not breach or violate any agreement you have with a former employer or any other third party. You further warrant and represent that all information provided to the Company or its agents with regard to your background is true and correct.

16.    You recognize that you will be subject to Spirit’s stock ownership guidelines and “clawback” policies as in effect from time to time.

As a confirmation of your agreement and acceptance of this offer, please sign and date below, and return this original offer letter to 2800 Executive Way, Miramar, Florida, 33025, attention: Laurie Villa.

Should you have any questions, please do not hesitate to let us know. We look forward to you joining us as we continue to build the first Ultra Low Cost Carrier in the Americas.

Sincerely,        

SPIRIT AIRLINES, INC.                 

/s/ Robert Fornaro

Robert Fornaro        Date: 7/25/16                

President & Chief Executive Officer

Agreed & Accepted,

/s/ Rocky B. Wiggins

Rocky B. Wiggins    Date: 7/25/16

.                    

3

EX-10.2

Exhibit 10.2

October 15, 2018

Scott Haralson

##############

##############

Dear Scott,

On behalf of Spirit Airlines, Inc. (“Spirit” or the “Company”), I would like to take this opportunity to confirm the terms of our offer of promotion to the Senior Vice President level. We are enthusiastic about your new position on the Spirit Team!

1. Your title will be Senior Vice President & Chief Financial Officer, and you will report directly to Ted Christie, President.

2. Your annualized base salary will be $325,000, which results in a semi-monthly payroll amount of $13,541.67 (gross – subject to withholdings for taxes and appropriate deductions). Your base salary will be subject to annual review in accordance with the Company’s executive compensation program and practices and your next annual review will be February 1, 2020.

3. You will be eligible to participate in the Company’s Short-Term Incentive Plan (STI) for Officers at the Senior Vice President (SVP) level beginning October 16^th, 2018.

a. Your STI target will change to 70% of base salary earnings effective October 16^th, 2018 paid during the 2018 STI plan year. From January 1^st, 2018 thru October 15^th, 2018 your STI target will remain at the Vice President level at 50% of base salary earnings over the period stated. Your actual STI payment can range from 0% to 200% of target depending on (i) the Company’s safety performance during the year, (ii) the Company’s performance under applicable financial and operational metrics and (iii) to the extent applicable, our Compensation Committee’s assessment of your individual performance. STI bonuses earned for any year are usually paid during the first calendar quarter of the following year. In no event will you be entitled to receive an STI payment for any year unless your employment with the Company continues through the date of payment except for termination due to death or permanent disability. Any STI plan payment is subject to the terms approved by the Compensation Committee of the Board.

4. Subject to approval by our Compensation Committee, you will be granted an initial off-cycle equity-based incentive award (the “Off-Cycle LTI Award”) having a grant face value of $50,000 (based on the average closing price of Spirit common stock for the 5 trading days prior to the date of grant). The Off-Cycle LTI Award will be subject to the terms and conditions of the Company’s 2015 Incentive Award Plan, as amended from time to time (“Incentive Award Plan”). The Off-Cycle LTI Award will be in the form of Restricted Stock Units, vesting over a four-year period as follows; 50% on the second anniversary of the grant date, 25% on the third anniversary of the grant date and the remaining 25% on the fourth anniversary of the grant date. Should your employment with the Company terminate for any reason (other than death or permanent disability) prior to the fourth anniversary of the grant date, the unvested portion of the Off-Cycle LTI Award would automatically terminate and forfeit at that time. It is

Page | 1

Exhibit 10.2

contemplated that the grant of the Off-Cycle LTI Award would be approved by our Compensation Committee at its first meeting following your promotion date or by written consent prior to this meeting.

5. Commencing in 2019, during your employment with the Company, you will be eligible to be granted annual long-term incentive equity awards (“Annual LTI Awards”) under the Incentive Award Plan. Your eligibility to receive an Annual LTI Award in any year will be on the basis, terms and conditions determined by the Compensation Committee in its discretion. It is contemplated that the 2019 Annual LTI Awards at the SVP level will have a grant date target range value of $225,000 to $675,000 and will be split 40/60 between Restricted Stock Units, vesting 25% annually over four years, and Performance Share Units, to be settled in shares of Company common stock after a three-year measurement period. Your Annual LTI Awards will be granted at the same time Annual LTI Awards are granted to other senior executive officers. Should your employment with the Company terminate for any reason (other than death or permanent disability) prior to the vesting date of any Annual LTI Award granted to you, the unvested portion of such Annual LTI Award will automatically terminate and forfeit at that time. The 2019 LTI award plan design is contingent upon approval by the Compensation Committee of the Board.

6. The Company may withhold from any compensation, reimbursements and benefits payable to you all taxes as required by law and well as other standard or customary withholdings and deductions. You also agree that target incentives do not constitute a promise of payment.

7. Under the Company’s current vacation pay policy, on your promotion date, you will continue to accrue vacation at a semi-monthly rate of 5.00 hours per pay period. If you worked an entire year, you would be eligible to accrue a maximum of three weeks. Of course, the Company may change or discontinue the policy at any time. All other welfare and 401K benefits will also remain the same as with your current employment.

8. As an officer of the Company, you will continue to be eligible for participation in the Spirit Airlines, Inc. 2017 Executive Severance Plan (as may be amended from time to time). In addition, as an officer of the Company, you will be covered by the Company's director and officer liability insurance policy, which may be changed or discontinued by the Company at any time.

9. Please note and understand that, consistent with Company practice, your employment with the Company constitutes “at will” employment and is not intended to be for a specified period. As a result, your employment with the Company may be terminated by you or the Company at any time, with or without cause and with or without advance notice.

10. As an employee of the Company, you will be expected and required to abide by the Company’s policies and procedures, including (but not limited to) the Company’s Code of Business Conduct and Ethics and Insider Trading Compliance Program. You also agree to comply with the covenants set forth in Annex A hereto, which is an integral part of this letter agreement.

11. This offer is contingent upon you signing and returning this letter to us no later than Tuesday, October 16^th, 2018.

12. You agree and warrant that in performing services for the Company, you will not use or disclose any confidential information of any prior employer or other person or entity. You further warrant and represent that you are able to fully and effectively perform your job functions for the Company without resort to, or reliance on, any such confidential information of any prior employer or other person or entity. You further warrant and represent that your acceptance of this promotion and your employment with the Company will not breach or violate any agreement you have with any third party. You further warrant and represent that all information previously provided to the Company or its agents with regard to your background is true and correct.

13. You recognize that you will be subject to Spirit’s stock ownership guidelines and “clawback” policies as in effect from time to time.

Page | 2

Exhibit 10.2

As a confirmation of your agreement and acceptance of this promotion offer, please sign and date below, and return this original offer letter to 2800 Executive Way, Miramar, Florida, 33025, attention Laurie Villa, SVP & CHRO.

Should you have any questions, please do not hesitate to let us know. We look forward to announcing your promotion and let me be the first to congratulate you on your promotion to SVP & CFO of Spirit Airlines.

Sincerely,        

/s/ Ted Christie

Ted Christie

President

Spirit Airlines, Inc.

Agreed & Accepted:

/s/ Scott Haralson

Scott Haralson            Date: 10/15/18

Attachment: Annex A

Page | 3

Exhibit 10.2

ANNEX A

Non-Solicitation. During Employee’s employment and for a period of one (1) year immediately following the termination thereof, regardless of the reason, timing or party who initiates termination of employment, Employee promises and agrees not to, directly or indirectly, either for Employee, or on behalf of or in coordination with, any other Person, solicit or hire any employee or former employee of Spirit or otherwise induce any employee of Spirit to terminate his or her employment.

Non-disparagement. Employee agrees and covenants that Employee will not at any time make, publish or communicate to any Person or in any public forum any defamatory or disparaging remarks, comments or statements concerning Spirit or its businesses, or any of its employees, officers, and existing and prospective customers, suppliers, investors and other associated third parties, or make any maliciously false statements about Spirit’s employees and officers.

Page | 4

EX-31.1

Exhibit 31.1

CERTIFICATION

I, Robert L. Fornaro, certify that:

1. I have reviewed this quarterly report on Form 10-Q of Spirit Airlines, Inc. (the "Registrant");

2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the Registrant as of, and for, the periods presented in this report;

4. The Registrant's other certifying officer and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as described in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the Registrant and have:

a) designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the Registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

b) designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

c) evaluated the effectiveness of the Registrant's disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and

d) disclosed in this report any change in the Registrant's internal control over financial reporting that occurred during the Registrant's most recent fiscal quarter (the Registrant's fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the Registrant's internal control over financial reporting; and

5. The Registrant's other certifying officer and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the Registrant's auditors and the audit committee of the Registrant's board of directors (or persons performing the equivalent functions):

a) all significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the Registrant's ability to record, process, summarize and report financial information; and

b) any fraud, whether or not material, that involves management or other employees who have a significant role in the Registrant's internal control over financial reporting.

Date: October 24, 2018	/s/ Robert L. Fornaro
	Robert L. Fornaro
	Chief Executive Officer

EX-31.2

Exhibit 31.2

CERTIFICATION

I, Scott M. Haralson, certify that:

1. I have reviewed this quarterly report on Form 10-Q of Spirit Airlines, Inc. (the "Registrant");

2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the Registrant as of, and for, the periods presented in this report;

4. The Registrant's other certifying officer and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as described in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the Registrant and have:

a) designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the Registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

b) designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

c) evaluated the effectiveness of the Registrant's disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and

d) disclosed in this report any change in the Registrant's internal control over financial reporting that occurred during the Company’s most recent fiscal quarter (the Registrant's fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the Registrant's internal control over financial reporting; and

5. The Registrant's other certifying officer and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the Registrant's auditors and the audit committee of the Registrant's board of directors (or persons performing the equivalent functions):

a) all significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the Registrant's ability to record, process, summarize and report financial information; and

b) any fraud, whether or not material, that involves management or other employees who have a significant role in the Registrant's internal control over financial reporting.

Date: October 24, 2018	/s/ Scott M. Haralson
	Scott M. Haralson
	Senior Vice President and Chief Financial Officer

EX-32.1

Exhibit 32.1

Certification of Chief Executive Officer Pursuant to 18 U.S.C. § 1350 As Adopted Pursuant to Section 906 of the Sarbanes-Oxley Act of 2002

Pursuant to 18 U.S.C. § 1350, adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, the undersigned officer of Spirit Airlines, Inc. (the “Company”) hereby certifies, to such officer’s knowledge, that:

(i.) the Quarterly Report on Form 10-Q of the Company for the quarter ended September 30, 2018 (the "Report") fully complies with the requirements of Section 13(a) or Section 15(d), as applicable, of the Securities Exchange Act of 1934, as amended; and

(ii.) the information contained in the Report fairly present, in all material respects, the financial condition and results of operations of the Company.

Date: October 24, 2018	/s/ Robert L. Fornaro
	Robert L. Fornaro
	Chief Executive Officer

EX-32.2

Exhibit 32.2

Certification of Chief Financial Officer Pursuant to 18 U.S.C. § 1350 As Adopted Pursuant to Section 906 of the Sarbanes-Oxley Act of 2002

Pursuant to 18 U.S.C. § 1350, adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, the undersigned officer of Spirit Airlines, Inc. (the “Company”) hereby certifies, to such officer’s knowledge, that:

(i.) the Quarterly Report on Form 10-Q of the Company for the quarter ended September 30, 2018 (the "Report") fully complies with the requirements of Section 13(a) or Section 15(d), as applicable, of the Securities Exchange Act of 1934, as amended; and

(ii.) the information contained in the Report fairly present, in all material respects, the financial condition and results of operations of the Company.

Date: October 24, 2018	/s/ Scott M. Haralson
	Scott M. Haralson
	Senior Vice President and Chief Financial Officer

XML

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 18, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Entity Registrant Name	SPIRIT AIRLINES, INC.
Entity Central Index Key	0001498710
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding		68,264,513

XML

Condensed Statements of Operations (unaudited) - USD ($) $ in Thousands	3 Months Ended							9 Months Ended		12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Operating revenues:
Revenues	$ 904,330	$ 851,771	$ 704,138	$ 666,182	$ 687,227	$ 700,185	$ 589,957	$ 2,460,239	$ 1,977,369	$ 2,643,552	$ 2,320,021
Operating expenses:
Aircraft fuel	258,818			175,205	158,300	142,294	139,782	709,644	440,376	615,581	447,553
Salaries, wages and benefits	185,043			136,815	134,114	129,892	127,138	527,895	391,144	527,959	472,471
Aircraft rent	42,682			42,820	53,396	52,566	57,070	134,618	163,032	205,852	201,675
Landing fees and other rents	54,542			46,117	48,498	45,592	40,448	162,774	134,538	180,655	151,679
Depreciation and amortization	43,773			36,472	36,840	35,331	31,509	128,764	103,680	140,152	101,136
Maintenance, materials and repairs	37,778			28,966	26,176	28,985	26,312	99,141	81,473	110,439	98,587
Distribution	37,868			28,170	29,695	29,835	25,772	103,496	85,302	113,472	96,895
Special charges (credits)	(686)			0	7,853	0	4,776	88,656	12,629	12,629	37,189
Loss on disposal of assets	1,069			1,054	516	1,493	1,105	6,561	3,114	4,168	4,187
Other operating	98,318			79,267	87,965	102,885	77,703	283,841	268,553	347,820	267,191
Total operating expenses	759,205			574,886	583,353	568,873	531,615	2,245,390	1,683,841	2,258,727	1,878,563
Operating income	145,125			91,296	103,874	131,312	58,342	214,849	293,528	384,825	441,458
Other (income) expense:
Interest expense	21,925			16,065	15,018	13,746	12,473	60,272	41,237	57,302	41,654
Capitalized interest	(2,657)			(3,668)	(3,203)	(3,342)	(3,580)	(7,205)	(10,125)	(13,793)	(12,705)
Interest income	(4,776)			(2,990)	(2,605)	(1,828)	(1,313)	(13,272)	(5,746)	(8,736)	(5,276)
Other expense	302			145	114	104	3	623	221	366	528
Special charges, non-operating	1,744				0			90,357	0
Total other (income) expense	16,538			9,552	9,324	8,680	7,583	130,775	25,587	35,139	24,201
Income before income taxes	128,587			81,744	94,550	122,632	50,759	84,074	267,941	349,686	417,257
Provision for income taxes	31,107			(165,231)	34,506	45,391	19,498	20,262	99,395	(65,836)	153,774
Net income	$ 97,480			$ 246,975	$ 60,044	$ 77,241	$ 31,261	$ 63,812	$ 168,546	$ 415,522	$ 263,483
Basic earnings per share	$ 1.43			$ 3.59	$ 0.87	$ 1.11	$ 0.45	$ 0.94	$ 2.43	$ 6.00	$ 3.75
Diluted earnings per share	$ 1.42			$ 3.58	$ 0.86	$ 1.11	$ 0.45	$ 0.93	$ 2.42	$ 5.99	$ 3.74
Passenger [Member]
Operating revenues:
Revenues	$ 887,956	836,350	689,141	$ 650,647	$ 669,072	$ 680,880	$ 572,287	$ 2,413,447	$ 1,922,239	$ 2,572,887	$ 2,257,801
Other [Member]
Operating revenues:
Revenues	$ 16,374	$ 15,421	$ 14,997	$ 15,535	$ 18,155	$ 19,305	$ 17,670	$ 46,792	$ 55,130	$ 70,665	$ 62,220

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Condensed Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 97,480	$ 60,044	$ 63,812	$ 168,546
Unrealized gain (loss) on short-term investment securities, net of deferred taxes of $(5), $7, $21 and ($6)	(7)	13	70	(11)
Interest rate derivative loss reclassified into earnings, net of taxes of $27, $31, $66 and $92	52	53	172	160
Other comprehensive income	45	66	242	149
Comprehensive income	$ 97,525	$ 60,110	$ 64,054	$ 168,695

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Condensed Statements of Comprehensive Income (Parenthetical) (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Tax effect of the unrealized gain (loss) on short-term investment securities	$ (5)	$ 7	$ 21	$ (6)
Loss reclassified from AOCI into earnings, tax	$ 27	$ 31	$ 66	$ 92

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Condensed Balance Sheets (unaudited) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 773,710	$ 800,849
Short-term investment securities	102,201	100,937
Accounts receivable, net	63,526	49,323
Aircraft maintenance deposits, net	104,472	175,615
Income tax receivable	78,506	69,844
Prepaid expenses and other current assets	83,692	85,542
Total current assets	1,206,107	1,282,110
Property and equipment:
Flight equipment	3,023,898	2,291,110
Ground property and equipment	178,339	155,166
Less accumulated depreciation	(296,157)	(207,808)
Total property and equipment	2,906,080	2,238,468
Deposits on flight equipment purchase contracts	253,825	253,687
Long-term aircraft maintenance deposits	144,642	150,617
Deferred heavy maintenance, net	191,632	99,915
Other long-term assets	79,445	121,003
Total assets	4,781,731	4,145,800
Current liabilities:
Accounts payable	63,190	22,822
Air traffic liability	323,627	263,711
Current maturities of long-term debt and capital leases	150,862	115,430
Other current liabilities	287,142	262,370
Total current liabilities	824,821	664,333
Long-term debt and capital leases, less current maturities	1,770,904	1,387,498
Deferred income taxes	332,119	308,814
Deferred gains and other long-term liabilities	20,105	22,581
Shareholders’ equity:
Common stock	7	7
Additional paid-in-capital	368,451	360,153
Treasury stock, at cost	(66,999)	(65,854)
Retained earnings	1,533,545	1,469,732
Accumulated other comprehensive income (loss)	(1,222)	(1,464)
Total shareholders’ equity	1,833,782	1,762,574
Total liabilities and shareholders’ equity	$ 4,781,731	$ 4,145,800

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Condensed Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating activities:
Net income	$ 63,812	$ 168,546
Adjustments to reconcile net income to net cash provided by operations:
Losses reclassified from other comprehensive income	238	252
Stock-based compensation	8,293	6,723
Allowance for doubtful accounts (recoveries)	(12)	(53)
Amortization of deferred gains and losses and debt issuance costs	6,508	6,415
Depreciation and amortization	128,764	103,680
Deferred income tax expense	21,243	97,833
Loss on disposal of assets	6,561	3,114
Lease termination costs	0	12,629
Special charges, non-operating	90,357	0
Changes in operating assets and liabilities:
Accounts receivable	(14,191)	(5,046)
Aircraft maintenance deposits, net	10,543	(28,422)
Prepaid income taxes	0	(160)
Long-term deposits and other assets	(5,760)	(69,307)
Deferred heavy maintenance	(121,643)	(12,032)
Income tax receivable	(8,662)	0
Accounts payable	38,771	13,829
Air traffic liability	59,916	73,639
Other liabilities	23,896	15,345
Other	(136)	339
Net cash provided by operating activities	308,498	387,324
Investing activities:
Purchase of available-for-sale investment securities	(100,228)	(96,851)
Proceeds from the maturity of available-for-sale investment securities	99,134	95,881
Proceeds from sale of property and equipment	9,500	0
Pre-delivery deposits for flight equipment, net of refunds	(132,297)	(121,702)
Capitalized interest	(6,116)	(8,054)
Purchase of property and equipment	(420,586)	(428,913)
Net cash used in investing activities	(550,593)	(559,639)
Financing activities:
Proceeds from issuance of long-term debt	518,171	405,827
Proceeds from stock options exercised	5	45
Payments on debt obligations	(93,225)	(63,352)
Payments on capital lease obligations	(205,566)	(291)
Repurchase of common stock	(1,145)	(1,238)
Debt issuance costs	(3,284)	(5,896)
Net cash provided by financing activities	214,956	335,095
Net (decrease) increase in cash and cash equivalents	(27,139)	162,780
Cash and cash equivalents at beginning of period	800,849	700,900
Cash and cash equivalents at end of period	773,710	863,680
Cash payments for:
Interest, net of capitalized interest	35,977	22,541
Income taxes paid, net of refunds	3,366	4,352
Non-cash transactions:
Capital expenditures funded by capital lease borrowings	$ (315)	$ (1,370)

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Basis of Presentation

9 Months Ended

Sep. 30, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Basis of Presentation

Basis of Presentation

The accompanying unaudited condensed financial statements include the accounts of Spirit Airlines, Inc. ("the Company"). These unaudited condensed financial statements reflect all normal recurring adjustments which management believes are necessary to fairly present the financial position, results of operations and cash flows of the Company for the respective periods presented. Certain information and footnote disclosures normally included in the annual financial statements prepared in accordance with U.S. generally accepted accounting principles ("GAAP") have been condensed or omitted pursuant to the rules and regulations of the Securities and Exchange Commission for Form 10-Q. These unaudited interim condensed financial statements should be read in conjunction with the audited financial statements of the Company and notes thereto included in the Company's Annual Report on Form 10-K for the year ended December 31, 2017 filed with the Securities and Exchange Commission on February 13, 2018.

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect both the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from these estimates.

The interim results reflected in the unaudited condensed financial statements are not necessarily indicative of the results that may be expected for other interim periods or for the full year.

Certain prior period amounts have been reclassified to conform to the current year's presentation and the adoption of Accounting Standards Update ("ASU") No. 2014-09, ("ASU 2014-09") "Revenue from Contracts with Customers".

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Recent Accounting Developments

9 Months Ended

Sep. 30, 2018

New Accounting Pronouncements and Changes in Accounting Principles [Abstract]

Recent Accounting Developments

Recent Accounting Developments

Recently Adopted Accounting Pronouncements

Revenue from Contracts with Customers

In May 2014, the Financial Accounting Standards Board ("the FASB") issued Accounting Standards Update ("ASU") No. 2014-09, ("ASU 2014-09") "Revenue from Contracts with Customers." The objective of ASU 2014-09 is to establish a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers. The Company adopted this guidance on January 1, 2018 utilizing the full retrospective method of adoption allowed by the standard, in order to provide for comparative results in all periods presented. The most significant impact of this ASU is the elimination of the incremental cost method for frequent flier program accounting, which requires the Company to re-value and record a liability associated with customer flight miles earned as part of the Company’s frequent flier program with a relative fair value approach. The classification and timing of recognition of certain ancillary fees is also impacted by the adoption of ASU 2014-09. While the adoption did not have a significant impact on earnings, the classification of certain revenues, such as bags, seats and other travel-related fees are now deemed part of the single performance obligation of providing passenger transportation. Refer to Note 3, Revenue Recognition for information regarding the Company's adoption of ASU 2014-09 and to Note 4, Revenue Disaggregation for the presentation of passenger revenues disaggregated by fare and non-fare.

Financial Instruments

In January 2016, the FASB issued ASU 2016-01, “Financial Instruments – Overall (Subtopic 825-10).” ASU 2016-01 makes several modifications to Subtopic 825-10 including the elimination of the available-for-sale classification of equity investments, and requires equity investments with readily determinable fair values to be measured at fair value with changes in fair value recognized in net income. ASU 2016-01 is effective for the Company for interim and annual periods beginning January 1, 2018. The Company adopted this guidance on January 1, 2018 with no material impact on the financial statements.

Statement of Cash Flows

In August 2016, the FASB issued ASU No. 2016-15, "Statement of Cash Flows." The standard is intended to reduce diversity in practice in how certain transactions are classified in the statement of cash flows. This standard is effective for the

Company for fiscal years, and interim periods within those years, beginning January 1, 2018. The Company adopted this guidance on January 1, 2018 with no material impact on the financial statements.

Recently Issued Accounting Pronouncements Not Yet Adopted

Leases

In February 2016, the FASB issued ASU No. 2016-02, "Leases (Topic 842)." This standard will require all lessees to recognize a right-of-use asset and a lease liability, initially measured at the present value of the lease payments, for all leases with a term greater than 12 months. The standard is effective for the Company effective January 1, 2019. Early adoption is permitted. However, the Company does not plan to early adopt. The Company has established a cross functional project plan and is in the process of testing items necessary to account for the new standard. The Company expects this standard to have a significant impact on its condensed balance sheets due to the recognition of right-of-use assets and lease liabilities for leases. The Company does not expect the adoption to have a significant impact on its lease classification, a material impact on its condensed statement of operations, or a notable impact on its liquidity. Additionally, the Company does not expect the standard to have a material impact on the Company’s debt-covenant compliance under its current agreements. Refer to Note 10, Commitments and Contingencies for information regarding the Company's undiscounted future lease payments and the timing of those payments. 

In July 2018, the FASB issued additional guidance on the accounting for leases. The guidance provides companies with another transition method that allows entities to recognize a cumulative-effect adjustment to the opening balance of retained earnings as of the date of adoption. Under this method, previously presented years’ financial positions and results would not be adjusted. The new guidance also provides lessors with a practical expedient, by class of underlying asset, to not separate non-lease components from the associated lease component if (1) the non-lease components would otherwise be accounted for under the new revenue recognition standard, (2) both the timing and pattern of transfer are the same for the non-lease components and associated lease component, and (3) if accounted for separately, the lease component would be classified as an operating lease. The Company is assessing the use of practical expedients in its accounting for leases.

Accounting for Credit Losses

In June 2016, the FASB issued ASU No. 2016-13, "Financial Instruments - Credit Losses." The standard requires the use of an "expected loss" model on certain types of financial instruments. The standard also amends the impairment model for available-for-sale securities and requires estimated credit losses to be recorded as allowances rather than as reductions to the amortized cost of the securities. This standard is effective for the Company for fiscal years, and interim periods within those years, beginning January 1, 2020, with early adoption permitted. The Company is evaluating the new guidance, but does not expect it to have a material impact on its financial statements.

Income Taxes

In March 2018, the FASB issued ASU 2018-05, Income Taxes ("Topic 740") - Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 118. The standard amends Accounting Standards Codification 740, Income Taxes ("ASC 740") to provide guidance on accounting for the tax effects of the Tax Cuts and Jobs Act (the "Tax Act") pursuant to Staff Accounting Bulletin No. 118. The provisional income tax amounts recorded may be affected as the Company gains a more thorough understanding of the tax law, including those related to the deductibility of acquired assets, state tax treatment and amounts related to employee compensation. The provisional accounting impacts for the Company may change in future reporting periods until the accounting is finalized, which will occur no later than the fourth quarter of 2018. The Company does not expect material changes to the financial statements in the fourth quarter of 2018 as a result of finalizing the accounting for the Tax Act.

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Revenue Recognition

9 Months Ended

Sep. 30, 2018

Revenue from Contract with Customer [Abstract]

Revenue Recognition

Revenue Recognition

Passenger revenues

Fare revenues. Tickets sold are initially deferred as “air traffic liability.” Passenger fare revenues are recognized at time of departure when transportation is provided. All tickets sold by the Company are nonrefundable. An unused ticket expires at the date of scheduled travel and is recognized as revenue at the date of scheduled travel. Passenger revenues reported prior to

the adoption of ASU 2014-09 are now reported as fare revenues within passenger revenues in the Company's disaggregated revenue table within Note 4, Revenue Disaggregation.

As of December 31, 2017 and 2016, the Company had air traffic liability ("ATL") balances of  $263.7 million and $220.2 million, respectively. As of September 30, 2018, all of the ATL balance as of December 31, 2017 has been recognized.

Non-fare revenues.The adoption of ASU 2014-09 impacted the classification of certain ancillary items such as bags, seats and other travel-related fees, since they are deemed part of the single performance obligation of providing passenger transportation. These ancillary items are now recognized in non-fare revenues within passenger revenues in the Company's disaggregated revenue table within Note 4, Revenue Disaggregation.

Changes and cancellations. Customers may elect to change or cancel their itinerary prior to the date of departure. For changes, a service charge is recognized at time of departure of newly scheduled travel and is deducted from the face value of the original purchase price of the ticket, and the original ticket becomes invalid. For cancellations, a service charge is assessed and the amount remaining after deducting the service charge is called a credit shell which generally expires 60 days from the date the credit shell is created and can be used towards the purchase of a new ticket and the Company’s other service offerings. Both the service charge and credit shell amounts are recorded as deferred revenue and amounts expected to expire unused are estimated based on historical experience. Estimating the amount of credits that will go unused involves some level of subjectivity and judgment. However, given the relatively short period of time to expiration, this does not have a significant impact on the Company's financial statements.

Other revenues

Other revenues primarily consist of the marketing component of the sale of frequent flyer miles to the Company's credit card partner and commissions revenue from the sale of various items such as hotels and rental cars.

Frequent Flyer Program

The Company's frequent flyer program generates customer loyalty by rewarding customers with mileage credits to travel on Spirit. When traveling, customers earn redeemable mileage credits for each mile flown on Spirit. Customers can also earn mileage credits through participating companies such as the co-branded Spirit credit card. Mileage credits are redeemable by customers in future periods for air travel on Spirit.

To reflect the mileage credits earned, the program includes two types of transactions that are considered revenue arrangements with multiple performance obligations: (1) mileage credits earned with travel and (2) mileage credits sold to co-branded credit card partner.

The adoption of ASU 2014-09 eliminated the incremental cost method for frequent flier program accounting, which required the Company to re-value and record a liability associated with customer flight miles earned with travel as part of the Company’s frequent flier program with a relative fair value. Upon adoption of ASU 2014-09 on January 1, 2018, the Company recorded an increase to its air traffic liability of $12.4 million.

Passenger ticket sales earning mileage credits. Passenger ticket sales earning mileage credits provide customers with (1) mileage credits earned and (2) air transportation. The Company values each performance obligation on a standalone basis. To value the mileage credits earned, the Company considers the quantitative value a passenger receives by redeeming miles for a ticket rather than paying cash, which is referred to as equivalent ticket value ("ETV").

The Company defers revenue for the mileage credits when earned and recognizes loyalty travel awards in passenger revenue as the miles are redeemed and services are provided. The Company records the air transportation portion of the passenger ticket sales in air traffic liability and recognizes passenger revenue when transportation is provided or if the ticket goes unused.

Sale of mileage credits. Customers may earn mileage credits based on their spending with the Company's co-branded credit card company with which the Company has an agreement to sell mileage credits. The contract to sell mileage credits under this agreement has multiple performance obligations. During the nine months ended September 30, 2018 and 2017, total cash sales from this agreement were $29.6 million and $38.1 million, respectively, which are allocated to travel and other performance obligations, as discussed below.

The Company's co-brand credit card agreement provides for joint marketing where cardholders earn mileage credits for making purchases using co-branded cards. During 2015, the Company extended its agreement with the administrator of the FREE SPIRIT affinity credit card program to extend through 2022. The Company accounts for this agreement consistently with the accounting method that allocates the consideration received to the individual products and services delivered. The value is allocated based on the relative selling prices of those products and services, which generally consists of (i) travel miles to be awarded, (ii) licensing of brand and access to member lists and (iii) advertising and marketing efforts. The Company determined the best estimate of the selling prices by considering discounted cash flow analysis using multiple inputs and assumptions, including: (1) the expected number of miles awarded and number of miles redeemed, (2) ETV for the award travel obligation, (3) licensing of brand and access to member lists and (4) advertising and marketing efforts. 

The Company defers the amount for award travel obligation as part of loyalty deferred revenue within air traffic liability on the balance sheet and recognizes loyalty travel awards in passenger revenue as the mileage credits are used for travel. Revenue allocated to the remaining performance obligations, primarily marketing components, is recorded in other revenue over time as miles are delivered.

Mileage breakage. For mileage credits that the Company estimates are not likely to be redeemed ("breakage"), the Company recognizes the associated value proportionally during the period in which the remaining mileage credits are redeemed. Management uses statistical models to estimate breakage based on historical redemption patterns. A change in assumptions as to the period over which mileage credits are expected to be redeemed, the actual redemption activity for mileage credits or the estimated fair value of mileage credits expected to be redeemed could have an impact on revenues in the year in which the change occurs and in future years.

Current activity of frequent flyer program. Mileage credits are combined in one homogeneous pool and are not separately identifiable. As such, revenue is comprised of miles that were part of the frequent flyer deferred revenue balance at the beginning of the period as well as miles that were issued during the period.

The following tables show adjustments made due to the adoption of ASU 2014-09 on the December 31, 2017 and 2016 statements of operations. Previously reported results were derived from audited financial statements included in Company's Annual Report on Form 10-K for the fiscal years ended December 31, 2017 and December 31, 2016, as applicable.

	Year Ended December 31, 2017
	(in thousands, except share and per share data)
	As Reported			Topic 606 Adjustment			As Adjusted
Operating revenues:
Passenger	$	1,366,034		$	1,206,853		$	2,572,887
Other	1,281,632			(1,210,967		)	70,665
Total operating revenues	2,647,666			(4,114		)	2,643,552
Operating expenses:
Aircraft fuel	615,581			—			615,581
Salaries, wages and benefits	527,959			—			527,959
Aircraft rent	205,852			—			205,852
Landing fees and other rents	180,655			—			180,655
Depreciation and amortization	140,152			—			140,152
Maintenance, materials and repairs	110,439			—			110,439
Distribution	113,620			(148		)	113,472
Special charges	12,629			—			12,629
Loss on disposal of assets	4,168			—			4,168
Other operating	347,820			—			347,820
Total operating expenses	2,258,875			(148		)	2,258,727
Operating income	388,791			(3,966		)	384,825
Other (income) expense:
Interest expense	57,302			—			57,302
Capitalized interest	(13,793		)	—			(13,793		)
Interest income	(8,736		)	—			(8,736		)
Other expense	366			—			366
Total other (income) expense	35,139			—			35,139
Income before income taxes	353,652			(3,966		)	349,686
Provision (benefit) for income taxes	(66,954		)	1,118			(65,836		)
Net income	$	420,606		$	(5,084	)	$	415,522
Basic earnings per share	$	6.08		$	(0.07	)	$	6.00
Diluted earnings per share	$	6.06		$	(0.07	)	$	5.99

	Year Ended December 31, 2016
	(in thousands, except share and per share data)
	As Reported			Topic 606 Adjustment			As Adjusted
Operating revenues:
Passenger	$	1,200,621		$	1,057,180		$	2,257,801
Other	1,121,335			(1,059,115		)	62,220
Total operating revenues	2,321,956			(1,935		)	2,320,021
Operating expenses:
Salaries, wages and benefits	472,471			—			472,471
Aircraft fuel	447,553			—			447,553
Aircraft rent	201,675			—			201,675
Landing fees and other rents	151,679			—			151,679
Depreciation and amortization	101,136			—			101,136
Maintenance, materials and repairs	98,587			—			98,587
Distribution	96,627			268			96,895
Special charges	37,189			—			37,189
Loss on disposal of assets	4,187			—			4,187
Other operating	267,191			—			267,191
Total operating expenses	1,878,295			268			1,878,563
Operating income	443,661			(2,203		)	441,458
Other (income) expense:
Interest expense	41,654			—			41,654
Capitalized interest	(12,705		)	—			(12,705		)
Interest income	(5,276		)	—			(5,276		)
Other expense	528			—			528
Total other (income) expense	24,201			—			24,201
Income before income taxes	419,460			(2,203		)	417,257
Provision (benefit) for income taxes	154,581			(807		)	153,774
Net income	$	264,879		$	(1,396	)	$	263,483
Basic earnings per share	$	3.77		$	(0.02	)	$	3.75
Diluted earnings per share	$	3.76		$	(0.02	)	$	3.74

The following table shows adjusted balances after the adoption of ASU 2014-09 on the quarterly statements of operations for each quarter of 2017.

	For the Quarter Ended
	March 31, 2017			June 30, 2017			September 30, 2017			December 31, 2017
	(in thousands, except share and per share data)
Operating revenues:
Passenger	$	572,287		$	680,880		$	669,072		$	650,647
Other	17,670			19,305			18,155			15,535
Total operating revenues	589,957			700,185			687,227			666,182
Operating expenses:
Aircraft fuel	139,782			142,294			158,300			175,205
Salaries, wages and benefits	127,138			129,892			134,114			136,815
Aircraft rent	57,070			52,566			53,396			42,820
Landing fees and other rents	40,448			45,592			48,498			46,117
Depreciation and amortization	31,509			35,331			36,840			36,472
Maintenance, materials and repairs	26,312			28,985			26,176			28,966
Distribution	25,772			29,835			29,695			28,170
Special charges	4,776			—			7,853			—
Loss on disposal of assets	1,105			1,493			516			1,054
Other operating	77,703			102,885			87,965			79,267
Total operating expenses	531,615			568,873			583,353			574,886
Operating income	58,342			131,312			103,874			91,296
Other (income) expense:
Interest expense	12,473			13,746			15,018			16,065
Capitalized interest	(3,580		)	(3,342		)	(3,203		)	(3,668		)
Interest income	(1,313		)	(1,828		)	(2,605		)	(2,990		)
Other expense	3			104			114			145
Total other (income) expense	7,583			8,680			9,324			9,552
Income before income taxes	50,759			122,632			94,550			81,744
Provision (benefit) for income taxes	19,498			45,391			34,506			(165,231		)
Net income	$	31,261		$	77,241		$	60,044		$	246,975
Basic earnings per share	$	0.45		$	1.11		$	0.87		$	3.59
Diluted earnings per share	$	0.45		$	1.11		$	0.86		$	3.58

The following table shows quarterly adjustments made due to the adoption of ASU 2014-09 on the statements of operations for 2017.

				Adjustments for the Quarter Ended
	Full Year 2017 As Reported			March 31, 2017			June 30, 2017			September 30, 2017			December 31, 2017			Full Year 2017 Adjusted
	(in thousands, except share and per share data)
Operating revenues:
Passenger	$	1,366,034		$	272,525		$	308,959		$	312,865		$	312,504		$	2,572,887
Other	1,281,632			(274,314		)	(310,455		)	(312,869		)	(313,329		)	70,665
Total operating revenues	2,647,666			(1,789		)	(1,496		)	(4		)	(825		)	2,643,552
Operating expenses:
Aircraft fuel	615,581			—			—			—			—			615,581
Salaries, wages and benefits	527,959			—			—			—			—			527,959
Aircraft rent	205,852			—			—			—			—			205,852
Landing fees and other rents	180,655			—			—			—			—			180,655
Depreciation and amortization	140,152			—			—			—			—			140,152
Maintenance, materials and repairs	110,439			—			—			—			—			110,439
Distribution	113,620			(726		)	(73		)	226			425			113,472
Special charges	12,629			—			—			—			—			12,629
Loss on disposal of assets	4,168			—			—			—			—			4,168
Other operating	347,820			—			—			—			—			347,820
Total operating expenses	2,258,875			(726		)	(73		)	226			425			2,258,727
Operating income	388,791			(1,063		)	(1,423		)	(230		)	(1,250		)	384,825
Other (income) expense:
Interest expense	57,302			—			—			—			—			57,302
Capitalized interest	(13,793		)	—			—			—			—			(13,793		)
Interest income	(8,736		)	—			—			—			—			(8,736		)
Other expense	366			—			—			—			—			366
Total other (income) expense	35,139			—			—			—			—			35,139
Income before income taxes	353,652			(1,063		)	(1,423		)	(230		)	(1,250		)	349,686
Provision (benefit) for income taxes	(66,954		)	(389		)	(522		)	(84		)	2,113			(65,836		)
Net income	$	420,606		$	(674	)	$	(901	)	$	(146	)	$	(3,363	)	$	415,522
Basic earnings per share	$	6.08		$	(0.01	)	$	(0.01	)	$	—		$	(0.05	)	$	6.00
Diluted earnings per share	$	6.06		$	(0.01	)	$	(0.01	)	$	—		$	(0.05	)	$	5.99

The following tables show adjustments made due to the adoption of ASU 2014-09 on the December 31, 2017 and 2016 balance sheets. Previously reported results were derived from audited financial statements included in Company's Annual Report on Form 10-K for the fiscal years ended December 31, 2017 and December 31, 2016, as applicable.

	December 31, 2017
	(in thousands)
	As Reported			Topic 606 Adjustment			As Adjusted
Assets
Current assets:
Cash and cash equivalents	$	800,849		$	—		$	800,849
Short-term investment securities	100,937			—			100,937
Accounts receivable, net	49,323			—			49,323
Aircraft maintenance deposits, net	175,615			—			175,615
Income tax receivable	69,844			—			69,844
Prepaid expenses and other current assets	83,692			1,850			85,542
Total current assets	1,280,260			1,850			1,282,110
Property and equipment:
Flight equipment	2,291,110			—			2,291,110
Ground property and equipment	155,166			—			155,166
Less accumulated depreciation	(207,808		)	—			(207,808		)
	2,238,468			—			2,238,468
Deposits on flight equipment purchase contracts	253,687			—			253,687
Long-term aircraft maintenance deposits	150,617			—			150,617
Deferred heavy maintenance, net	99,915			—			99,915
Other long-term assets	121,003			—			121,003
Total assets	$	4,143,950		$	1,850		$	4,145,800
Liabilities and shareholders’ equity
Current liabilities:
Accounts payable	$	22,822		$	—		$	22,822
Air traffic liability	246,404			17,307			263,711
Current maturities of long-term debt	115,430			—			115,430
Other current liabilities	262,370			—			262,370
Total current liabilities	647,026			17,307			664,333
Long-term debt, less current maturities	1,387,498			—			1,387,498
Deferred income taxes	313,140			(4,326		)	308,814
Deferred gains and other long-term liabilities	19,205			3,376			22,581
Shareholders’ equity:
Common stock: Common stock, $0.0001 par value, 240,000,000 shares authorized at December 31, 2017; 69,770,795 issued and 68,196,964 outstanding as of December 31, 2017	7			—			7
Additional paid-in-capital	360,153			—			360,153
Treasury stock, at cost: 1,573,831 shares as of December 31, 2017	(65,854		)	—			(65,854		)
Retained earnings	1,484,239			(14,507		)	1,469,732
Accumulated other comprehensive income (loss)	(1,464		)	—			(1,464		)
Total shareholders’ equity	1,777,081			(14,507		)	1,762,574
Total liabilities and shareholders’ equity	$	4,143,950		$	1,850		$	4,145,800

	December 31, 2016
	(in thousands)
	As Reported			Topic 606 Adjustment			As Adjusted
Assets
Current assets:
Cash and cash equivalents	$	700,900		$	—		$	700,900
Short-term investment securities	100,155			—			100,155
Accounts receivable, net	41,136			—			41,136
Aircraft maintenance deposits, net	87,035			—			87,035
Income tax receivable	—			—			—
Prepaid expenses and other current assets	46,619			1,702			48,321
Total current assets	975,845			1,702			977,547
Property and equipment:
Flight equipment	1,461,525			—			1,461,525
Ground property and equipment	126,206			—			126,206
Less accumulated depreciation	(122,509		)	—			(122,509		)
	1,465,222			—			1,465,222
Deposits on flight equipment purchase contracts	325,688			—			325,688
Long-term aircraft maintenance deposits	199,415			—			199,415
Deferred heavy maintenance, net	75,534			—			75,534
Other long-term assets	110,223			—			110,223
Total assets	$	3,151,927		$	1,702		$	3,153,629
Liabilities and shareholders’ equity
Current liabilities:
Accounts payable	$	15,193		$	—		$	15,193
Air traffic liability	206,392			13,792			220,184
Current maturities of long-term debt	84,354			—			84,354
Other current liabilities	226,011			—			226,011
Total current liabilities	531,950			13,792			545,742
Long-term debt, less current maturities	897,359			—			897,359
Deferred income taxes	308,143			(5,443		)	302,700
Deferred gains and other long-term liabilities	19,868			2,776			22,644
Shareholders’ equity:
Common stock: Common stock, $0.0001 par value, 240,000,000 shares authorized at December 31, 2016; 73,549,872 issued and 69,326,202 outstanding as of December 31, 2016	7			—			7
Additional paid-in-capital	551,004			—			551,004
Treasury stock, at cost: 4,223,670 shares as of December 31, 2016	(218,692		)	—			(218,692		)
Retained earnings	1,063,633			(9,423		)	1,054,210
Accumulated other comprehensive income (loss)	(1,345		)	—			(1,345		)
Total shareholders’ equity	1,394,607			(9,423		)	1,385,184
Total liabilities and shareholders’ equity	$	3,151,927		$	1,702		$	3,153,629

Revenue Disaggregation

Operating revenues is comprised of passenger revenues, which includes fare and non-fare revenues, and other revenues. The following table shows disaggregated operating revenues for each quarter of 2018 and 2017.

	For the Quarter Ended
	September 30, 2018		June 30, 2018		March 31, 2018		December 31, 2017		September 30, 2017		June 30, 2017		March 31, 2017
	(in thousands)
Operating revenues:
Fare	$	476,660	$	439,549	$	342,695	$	337,324	$	355,593	$	371,443	$	299,035
Non-fare	411,296		396,801		346,446		313,323		313,479		309,437		273,252
Total passenger revenues	887,956		836,350		689,141		650,647		669,072		680,880		572,287
Other revenues	16,374		15,421		14,997		15,535		18,155		19,305		17,670
Total operating revenues	$	904,330	$	851,771	$	704,138	$	666,182	$	687,227	$	700,185	$	589,957

The following table shows disaggregated operating revenues for years ended December 31, 2017 and 2016.    

	Year Ended December 31,
	2017							2016
	(in thousands)
	As Reported		Topic 606 Adjustment			As Adjusted		As Reported		Topic 606 Adjustment			As Adjusted
Operating revenues:
Fare	$	1,366,034	$	(2,639	)	$	1,363,395	$	1,200,621	$	(2,514	)	$	1,198,107
Non-fare	—		1,209,492			1,209,492		—		1,059,694			1,059,694
Total passenger revenues	1,366,034		1,206,853			2,572,887		1,200,621		1,057,180			2,257,801
Other revenues	1,281,632		(1,210,967		)	70,665		1,121,335		(1,059,115		)	62,220
Total operating revenues	$	2,647,666	$	(4,114	)	$	2,643,552	$	2,321,956	$	(1,935	)	$	2,320,021

The Company is managed as a single business unit that provides air transportation for passengers. Operating revenues by geographic region as defined by the Department of Transportation ("DOT") area are summarized below:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
	(in millions)
DOT—Domestic	$	819.3	$	636.3	$	2,236.3	$	1,819.2
DOT—Latin America	85.0		50.9		223.9		158.2
Total	$	904.3	$	687.2	$	2,460.2	$	1,977.4

XML

Revenue Disaggregation

9 Months Ended

Sep. 30, 2018

Revenue from Contract with Customer [Abstract]

Revenue Disaggregation

Revenue Recognition

Passenger revenues

Fare revenues. Tickets sold are initially deferred as “air traffic liability.” Passenger fare revenues are recognized at time of departure when transportation is provided. All tickets sold by the Company are nonrefundable. An unused ticket expires at the date of scheduled travel and is recognized as revenue at the date of scheduled travel. Passenger revenues reported prior to

the adoption of ASU 2014-09 are now reported as fare revenues within passenger revenues in the Company's disaggregated revenue table within Note 4, Revenue Disaggregation.

As of December 31, 2017 and 2016, the Company had air traffic liability ("ATL") balances of  $263.7 million and $220.2 million, respectively. As of September 30, 2018, all of the ATL balance as of December 31, 2017 has been recognized.

Non-fare revenues.The adoption of ASU 2014-09 impacted the classification of certain ancillary items such as bags, seats and other travel-related fees, since they are deemed part of the single performance obligation of providing passenger transportation. These ancillary items are now recognized in non-fare revenues within passenger revenues in the Company's disaggregated revenue table within Note 4, Revenue Disaggregation.

Changes and cancellations. Customers may elect to change or cancel their itinerary prior to the date of departure. For changes, a service charge is recognized at time of departure of newly scheduled travel and is deducted from the face value of the original purchase price of the ticket, and the original ticket becomes invalid. For cancellations, a service charge is assessed and the amount remaining after deducting the service charge is called a credit shell which generally expires 60 days from the date the credit shell is created and can be used towards the purchase of a new ticket and the Company’s other service offerings. Both the service charge and credit shell amounts are recorded as deferred revenue and amounts expected to expire unused are estimated based on historical experience. Estimating the amount of credits that will go unused involves some level of subjectivity and judgment. However, given the relatively short period of time to expiration, this does not have a significant impact on the Company's financial statements.

Other revenues

Other revenues primarily consist of the marketing component of the sale of frequent flyer miles to the Company's credit card partner and commissions revenue from the sale of various items such as hotels and rental cars.

Frequent Flyer Program

The Company's frequent flyer program generates customer loyalty by rewarding customers with mileage credits to travel on Spirit. When traveling, customers earn redeemable mileage credits for each mile flown on Spirit. Customers can also earn mileage credits through participating companies such as the co-branded Spirit credit card. Mileage credits are redeemable by customers in future periods for air travel on Spirit.

To reflect the mileage credits earned, the program includes two types of transactions that are considered revenue arrangements with multiple performance obligations: (1) mileage credits earned with travel and (2) mileage credits sold to co-branded credit card partner.

The adoption of ASU 2014-09 eliminated the incremental cost method for frequent flier program accounting, which required the Company to re-value and record a liability associated with customer flight miles earned with travel as part of the Company’s frequent flier program with a relative fair value. Upon adoption of ASU 2014-09 on January 1, 2018, the Company recorded an increase to its air traffic liability of $12.4 million.

Passenger ticket sales earning mileage credits. Passenger ticket sales earning mileage credits provide customers with (1) mileage credits earned and (2) air transportation. The Company values each performance obligation on a standalone basis. To value the mileage credits earned, the Company considers the quantitative value a passenger receives by redeeming miles for a ticket rather than paying cash, which is referred to as equivalent ticket value ("ETV").

The Company defers revenue for the mileage credits when earned and recognizes loyalty travel awards in passenger revenue as the miles are redeemed and services are provided. The Company records the air transportation portion of the passenger ticket sales in air traffic liability and recognizes passenger revenue when transportation is provided or if the ticket goes unused.

Sale of mileage credits. Customers may earn mileage credits based on their spending with the Company's co-branded credit card company with which the Company has an agreement to sell mileage credits. The contract to sell mileage credits under this agreement has multiple performance obligations. During the nine months ended September 30, 2018 and 2017, total cash sales from this agreement were $29.6 million and $38.1 million, respectively, which are allocated to travel and other performance obligations, as discussed below.

The Company's co-brand credit card agreement provides for joint marketing where cardholders earn mileage credits for making purchases using co-branded cards. During 2015, the Company extended its agreement with the administrator of the FREE SPIRIT affinity credit card program to extend through 2022. The Company accounts for this agreement consistently with the accounting method that allocates the consideration received to the individual products and services delivered. The value is allocated based on the relative selling prices of those products and services, which generally consists of (i) travel miles to be awarded, (ii) licensing of brand and access to member lists and (iii) advertising and marketing efforts. The Company determined the best estimate of the selling prices by considering discounted cash flow analysis using multiple inputs and assumptions, including: (1) the expected number of miles awarded and number of miles redeemed, (2) ETV for the award travel obligation, (3) licensing of brand and access to member lists and (4) advertising and marketing efforts. 

The Company defers the amount for award travel obligation as part of loyalty deferred revenue within air traffic liability on the balance sheet and recognizes loyalty travel awards in passenger revenue as the mileage credits are used for travel. Revenue allocated to the remaining performance obligations, primarily marketing components, is recorded in other revenue over time as miles are delivered.

Mileage breakage. For mileage credits that the Company estimates are not likely to be redeemed ("breakage"), the Company recognizes the associated value proportionally during the period in which the remaining mileage credits are redeemed. Management uses statistical models to estimate breakage based on historical redemption patterns. A change in assumptions as to the period over which mileage credits are expected to be redeemed, the actual redemption activity for mileage credits or the estimated fair value of mileage credits expected to be redeemed could have an impact on revenues in the year in which the change occurs and in future years.

Current activity of frequent flyer program. Mileage credits are combined in one homogeneous pool and are not separately identifiable. As such, revenue is comprised of miles that were part of the frequent flyer deferred revenue balance at the beginning of the period as well as miles that were issued during the period.

The following tables show adjustments made due to the adoption of ASU 2014-09 on the December 31, 2017 and 2016 statements of operations. Previously reported results were derived from audited financial statements included in Company's Annual Report on Form 10-K for the fiscal years ended December 31, 2017 and December 31, 2016, as applicable.

	Year Ended December 31, 2017
	(in thousands, except share and per share data)
	As Reported			Topic 606 Adjustment			As Adjusted
Operating revenues:
Passenger	$	1,366,034		$	1,206,853		$	2,572,887
Other	1,281,632			(1,210,967		)	70,665
Total operating revenues	2,647,666			(4,114		)	2,643,552
Operating expenses:
Aircraft fuel	615,581			—			615,581
Salaries, wages and benefits	527,959			—			527,959
Aircraft rent	205,852			—			205,852
Landing fees and other rents	180,655			—			180,655
Depreciation and amortization	140,152			—			140,152
Maintenance, materials and repairs	110,439			—			110,439
Distribution	113,620			(148		)	113,472
Special charges	12,629			—			12,629
Loss on disposal of assets	4,168			—			4,168
Other operating	347,820			—			347,820
Total operating expenses	2,258,875			(148		)	2,258,727
Operating income	388,791			(3,966		)	384,825
Other (income) expense:
Interest expense	57,302			—			57,302
Capitalized interest	(13,793		)	—			(13,793		)
Interest income	(8,736		)	—			(8,736		)
Other expense	366			—			366
Total other (income) expense	35,139			—			35,139
Income before income taxes	353,652			(3,966		)	349,686
Provision (benefit) for income taxes	(66,954		)	1,118			(65,836		)
Net income	$	420,606		$	(5,084	)	$	415,522
Basic earnings per share	$	6.08		$	(0.07	)	$	6.00
Diluted earnings per share	$	6.06		$	(0.07	)	$	5.99

	Year Ended December 31, 2016
	(in thousands, except share and per share data)
	As Reported			Topic 606 Adjustment			As Adjusted
Operating revenues:
Passenger	$	1,200,621		$	1,057,180		$	2,257,801
Other	1,121,335			(1,059,115		)	62,220
Total operating revenues	2,321,956			(1,935		)	2,320,021
Operating expenses:
Salaries, wages and benefits	472,471			—			472,471
Aircraft fuel	447,553			—			447,553
Aircraft rent	201,675			—			201,675
Landing fees and other rents	151,679			—			151,679
Depreciation and amortization	101,136			—			101,136
Maintenance, materials and repairs	98,587			—			98,587
Distribution	96,627			268			96,895
Special charges	37,189			—			37,189
Loss on disposal of assets	4,187			—			4,187
Other operating	267,191			—			267,191
Total operating expenses	1,878,295			268			1,878,563
Operating income	443,661			(2,203		)	441,458
Other (income) expense:
Interest expense	41,654			—			41,654
Capitalized interest	(12,705		)	—			(12,705		)
Interest income	(5,276		)	—			(5,276		)
Other expense	528			—			528
Total other (income) expense	24,201			—			24,201
Income before income taxes	419,460			(2,203		)	417,257
Provision (benefit) for income taxes	154,581			(807		)	153,774
Net income	$	264,879		$	(1,396	)	$	263,483
Basic earnings per share	$	3.77		$	(0.02	)	$	3.75
Diluted earnings per share	$	3.76		$	(0.02	)	$	3.74

The following table shows adjusted balances after the adoption of ASU 2014-09 on the quarterly statements of operations for each quarter of 2017.

	For the Quarter Ended
	March 31, 2017			June 30, 2017			September 30, 2017			December 31, 2017
	(in thousands, except share and per share data)
Operating revenues:
Passenger	$	572,287		$	680,880		$	669,072		$	650,647
Other	17,670			19,305			18,155			15,535
Total operating revenues	589,957			700,185			687,227			666,182
Operating expenses:
Aircraft fuel	139,782			142,294			158,300			175,205
Salaries, wages and benefits	127,138			129,892			134,114			136,815
Aircraft rent	57,070			52,566			53,396			42,820
Landing fees and other rents	40,448			45,592			48,498			46,117
Depreciation and amortization	31,509			35,331			36,840			36,472
Maintenance, materials and repairs	26,312			28,985			26,176			28,966
Distribution	25,772			29,835			29,695			28,170
Special charges	4,776			—			7,853			—
Loss on disposal of assets	1,105			1,493			516			1,054
Other operating	77,703			102,885			87,965			79,267
Total operating expenses	531,615			568,873			583,353			574,886
Operating income	58,342			131,312			103,874			91,296
Other (income) expense:
Interest expense	12,473			13,746			15,018			16,065
Capitalized interest	(3,580		)	(3,342		)	(3,203		)	(3,668		)
Interest income	(1,313		)	(1,828		)	(2,605		)	(2,990		)
Other expense	3			104			114			145
Total other (income) expense	7,583			8,680			9,324			9,552
Income before income taxes	50,759			122,632			94,550			81,744
Provision (benefit) for income taxes	19,498			45,391			34,506			(165,231		)
Net income	$	31,261		$	77,241		$	60,044		$	246,975
Basic earnings per share	$	0.45		$	1.11		$	0.87		$	3.59
Diluted earnings per share	$	0.45		$	1.11		$	0.86		$	3.58

The following table shows quarterly adjustments made due to the adoption of ASU 2014-09 on the statements of operations for 2017.

				Adjustments for the Quarter Ended
	Full Year 2017 As Reported			March 31, 2017			June 30, 2017			September 30, 2017			December 31, 2017			Full Year 2017 Adjusted
	(in thousands, except share and per share data)
Operating revenues:
Passenger	$	1,366,034		$	272,525		$	308,959		$	312,865		$	312,504		$	2,572,887
Other	1,281,632			(274,314		)	(310,455		)	(312,869		)	(313,329		)	70,665
Total operating revenues	2,647,666			(1,789		)	(1,496		)	(4		)	(825		)	2,643,552
Operating expenses:
Aircraft fuel	615,581			—			—			—			—			615,581
Salaries, wages and benefits	527,959			—			—			—			—			527,959
Aircraft rent	205,852			—			—			—			—			205,852
Landing fees and other rents	180,655			—			—			—			—			180,655
Depreciation and amortization	140,152			—			—			—			—			140,152
Maintenance, materials and repairs	110,439			—			—			—			—			110,439
Distribution	113,620			(726		)	(73		)	226			425			113,472
Special charges	12,629			—			—			—			—			12,629
Loss on disposal of assets	4,168			—			—			—			—			4,168
Other operating	347,820			—			—			—			—			347,820
Total operating expenses	2,258,875			(726		)	(73		)	226			425			2,258,727
Operating income	388,791			(1,063		)	(1,423		)	(230		)	(1,250		)	384,825
Other (income) expense:
Interest expense	57,302			—			—			—			—			57,302
Capitalized interest	(13,793		)	—			—			—			—			(13,793		)
Interest income	(8,736		)	—			—			—			—			(8,736		)
Other expense	366			—			—			—			—			366
Total other (income) expense	35,139			—			—			—			—			35,139
Income before income taxes	353,652			(1,063		)	(1,423		)	(230		)	(1,250		)	349,686
Provision (benefit) for income taxes	(66,954		)	(389		)	(522		)	(84		)	2,113			(65,836		)
Net income	$	420,606		$	(674	)	$	(901	)	$	(146	)	$	(3,363	)	$	415,522
Basic earnings per share	$	6.08		$	(0.01	)	$	(0.01	)	$	—		$	(0.05	)	$	6.00
Diluted earnings per share	$	6.06		$	(0.01	)	$	(0.01	)	$	—		$	(0.05	)	$	5.99

The following tables show adjustments made due to the adoption of ASU 2014-09 on the December 31, 2017 and 2016 balance sheets. Previously reported results were derived from audited financial statements included in Company's Annual Report on Form 10-K for the fiscal years ended December 31, 2017 and December 31, 2016, as applicable.

	December 31, 2017
	(in thousands)
	As Reported			Topic 606 Adjustment			As Adjusted
Assets
Current assets:
Cash and cash equivalents	$	800,849		$	—		$	800,849
Short-term investment securities	100,937			—			100,937
Accounts receivable, net	49,323			—			49,323
Aircraft maintenance deposits, net	175,615			—			175,615
Income tax receivable	69,844			—			69,844
Prepaid expenses and other current assets	83,692			1,850			85,542
Total current assets	1,280,260			1,850			1,282,110
Property and equipment:
Flight equipment	2,291,110			—			2,291,110
Ground property and equipment	155,166			—			155,166
Less accumulated depreciation	(207,808		)	—			(207,808		)
	2,238,468			—			2,238,468
Deposits on flight equipment purchase contracts	253,687			—			253,687
Long-term aircraft maintenance deposits	150,617			—			150,617
Deferred heavy maintenance, net	99,915			—			99,915
Other long-term assets	121,003			—			121,003
Total assets	$	4,143,950		$	1,850		$	4,145,800
Liabilities and shareholders’ equity
Current liabilities:
Accounts payable	$	22,822		$	—		$	22,822
Air traffic liability	246,404			17,307			263,711
Current maturities of long-term debt	115,430			—			115,430
Other current liabilities	262,370			—			262,370
Total current liabilities	647,026			17,307			664,333
Long-term debt, less current maturities	1,387,498			—			1,387,498
Deferred income taxes	313,140			(4,326		)	308,814
Deferred gains and other long-term liabilities	19,205			3,376			22,581
Shareholders’ equity:
Common stock: Common stock, $0.0001 par value, 240,000,000 shares authorized at December 31, 2017; 69,770,795 issued and 68,196,964 outstanding as of December 31, 2017	7			—			7
Additional paid-in-capital	360,153			—			360,153
Treasury stock, at cost: 1,573,831 shares as of December 31, 2017	(65,854		)	—			(65,854		)
Retained earnings	1,484,239			(14,507		)	1,469,732
Accumulated other comprehensive income (loss)	(1,464		)	—			(1,464		)
Total shareholders’ equity	1,777,081			(14,507		)	1,762,574
Total liabilities and shareholders’ equity	$	4,143,950		$	1,850		$	4,145,800

	December 31, 2016
	(in thousands)
	As Reported			Topic 606 Adjustment			As Adjusted
Assets
Current assets:
Cash and cash equivalents	$	700,900		$	—		$	700,900
Short-term investment securities	100,155			—			100,155
Accounts receivable, net	41,136			—			41,136
Aircraft maintenance deposits, net	87,035			—			87,035
Income tax receivable	—			—			—
Prepaid expenses and other current assets	46,619			1,702			48,321
Total current assets	975,845			1,702			977,547
Property and equipment:
Flight equipment	1,461,525			—			1,461,525
Ground property and equipment	126,206			—			126,206
Less accumulated depreciation	(122,509		)	—			(122,509		)
	1,465,222			—			1,465,222
Deposits on flight equipment purchase contracts	325,688			—			325,688
Long-term aircraft maintenance deposits	199,415			—			199,415
Deferred heavy maintenance, net	75,534			—			75,534
Other long-term assets	110,223			—			110,223
Total assets	$	3,151,927		$	1,702		$	3,153,629
Liabilities and shareholders’ equity
Current liabilities:
Accounts payable	$	15,193		$	—		$	15,193
Air traffic liability	206,392			13,792			220,184
Current maturities of long-term debt	84,354			—			84,354
Other current liabilities	226,011			—			226,011
Total current liabilities	531,950			13,792			545,742
Long-term debt, less current maturities	897,359			—			897,359
Deferred income taxes	308,143			(5,443		)	302,700
Deferred gains and other long-term liabilities	19,868			2,776			22,644
Shareholders’ equity:
Common stock: Common stock, $0.0001 par value, 240,000,000 shares authorized at December 31, 2016; 73,549,872 issued and 69,326,202 outstanding as of December 31, 2016	7			—			7
Additional paid-in-capital	551,004			—			551,004
Treasury stock, at cost: 4,223,670 shares as of December 31, 2016	(218,692		)	—			(218,692		)
Retained earnings	1,063,633			(9,423		)	1,054,210
Accumulated other comprehensive income (loss)	(1,345		)	—			(1,345		)
Total shareholders’ equity	1,394,607			(9,423		)	1,385,184
Total liabilities and shareholders’ equity	$	3,151,927		$	1,702		$	3,153,629

Revenue Disaggregation

Operating revenues is comprised of passenger revenues, which includes fare and non-fare revenues, and other revenues. The following table shows disaggregated operating revenues for each quarter of 2018 and 2017.

	For the Quarter Ended
	September 30, 2018		June 30, 2018		March 31, 2018		December 31, 2017		September 30, 2017		June 30, 2017		March 31, 2017
	(in thousands)
Operating revenues:
Fare	$	476,660	$	439,549	$	342,695	$	337,324	$	355,593	$	371,443	$	299,035
Non-fare	411,296		396,801		346,446		313,323		313,479		309,437		273,252
Total passenger revenues	887,956		836,350		689,141		650,647		669,072		680,880		572,287
Other revenues	16,374		15,421		14,997		15,535		18,155		19,305		17,670
Total operating revenues	$	904,330	$	851,771	$	704,138	$	666,182	$	687,227	$	700,185	$	589,957

The following table shows disaggregated operating revenues for years ended December 31, 2017 and 2016.    

	Year Ended December 31,
	2017							2016
	(in thousands)
	As Reported		Topic 606 Adjustment			As Adjusted		As Reported		Topic 606 Adjustment			As Adjusted
Operating revenues:
Fare	$	1,366,034	$	(2,639	)	$	1,363,395	$	1,200,621	$	(2,514	)	$	1,198,107
Non-fare	—		1,209,492			1,209,492		—		1,059,694			1,059,694
Total passenger revenues	1,366,034		1,206,853			2,572,887		1,200,621		1,057,180			2,257,801
Other revenues	1,281,632		(1,210,967		)	70,665		1,121,335		(1,059,115		)	62,220
Total operating revenues	$	2,647,666	$	(4,114	)	$	2,643,552	$	2,321,956	$	(1,935	)	$	2,320,021

The Company is managed as a single business unit that provides air transportation for passengers. Operating revenues by geographic region as defined by the Department of Transportation ("DOT") area are summarized below:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
	(in millions)
DOT—Domestic	$	819.3	$	636.3	$	2,236.3	$	1,819.2
DOT—Latin America	85.0		50.9		223.9		158.2
Total	$	904.3	$	687.2	$	2,460.2	$	1,977.4

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Special Charges

9 Months Ended

Sep. 30, 2018

Special Charges and Credits [Abstract]

Special Charges

Special Charges

Special Charges (Credits), Operating

During the first quarter of 2018, the Company negotiated and amended the collective bargaining agreement with the Air Line Pilots Association, International ("ALPA"), under the guidance of the National Mediation Board ("NMB"). In

connection with the amended agreement, the Company incurred a one-time ratification incentive of $80.2 million, including payroll taxes, and an $8.5 million adjustment related to other contractual provisions. As a result, the Company recorded $88.7 million in special charges (credits) within operating expenses in the condensed statement of operations for the nine months ended September 30, 2018. As of September 30, 2018, the Company has paid $76.2 million of the ratification incentive with the remainder expected to be paid during the fourth quarter of 2018.

During the nine months ended September 30, 2017, the Company purchased one engine and one aircraft which were previously financed under operating lease agreements. The purchase price of the 1 engine and 1 aircraft was $8.1 million and $20.0 million, respectively, comprised of a cash payment of $3.8 million and $12.6 million, respectively, and the non-cash application of maintenance reserves and security deposits held by the previous lessor of $4.3 million and $7.4 million, respectively. The Company estimated the fair value of the engine and aircraft to be $3.1 million and $11.9 million, respectively, and has recorded the 1 purchased engine and 1 aircraft at fair value within flight equipment on the condensed balance sheets. The Company determined the valuation of the engine and aircraft based on a third-party appraisal considering the condition of the engine and aircraft (a Level 3 measurement). The Company recognized $4.8 million and $7.9 million as a cost of terminating the lease within special charges (credits) in the condensed statement of operations, respectively, made up of the excess of the purchase price paid over the fair value of the engine and the aircraft, less other non-cash items of $0.2 million and $0.2 million, respectively.

Special Charges, Non-Operating

During the nine months ended September 30, 2018, the Company recorded $90.4 million, in special charges, non-operating within other (income) expense in the statement of operations. During the first quarter of 2018, the Company entered into an aircraft purchase agreement for the purchase of 14 A319 aircraft previously operated under operating leases by the Company. The aggregate gross purchase price for the 14 aircraft was $285.0 million, and the price for each aircraft at the time of the sale was comprised of a cash payment net of the amount of maintenance reserves and security deposits for such aircraft held by the applicable lessor pursuant to the lease for such aircraft. The contract was deemed a lease modification which resulted in a change of classification from operating leases to capital leases for the 14 aircraft. During the first quarter of 2018, the capital lease assets were recorded at the lower of cost or fair value of the aircraft within flight equipment on the condensed balance sheets. During the second quarter of 2018, the purchase of the 14 aircraft was completed and the obligation was accreted up to the net cash payment price with interest charges recognized in special charges, non-operating in the statement of operations. The Company determined the valuation of the aircraft based on third-party appraisals considering the condition of the aircraft (a Level 3 measurement).

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Earnings per Share

9 Months Ended

Sep. 30, 2018

Earnings Per Share [Abstract]

Earnings per Share

Earnings per Share

The following table sets forth the computation of basic and diluted earnings per common share:

 

	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
	(in thousands, except per share amounts)
Numerator
Net income	$	97,480	$	60,044	$	63,812	$	168,546
Denominator
Weighted-average shares outstanding, basic	68,254		69,370		68,243		69,363
Effect of dilutive stock awards	249		88		103		174
Adjusted weighted-average shares outstanding, diluted	68,503		69,458		68,346		69,537
Net income per share
Basic earnings per common share	$	1.43	$	0.87	$	0.94	$	2.43
Diluted earnings per common share	$	1.42	$	0.86	$	0.93	$	2.42
Anti-dilutive weighted-average shares	5		124		192		76

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Short-term Investment Securities

9 Months Ended

Sep. 30, 2018

Investments, Debt and Equity Securities [Abstract]

Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block]

Short-term Investment Securities

The Company's short-term investment securities are classified as available-for-sale and consist of U.S. Treasury and U.S. government agency securities with contractual maturities of 12 months or less. These securities are stated at fair value within current assets on the Company's condensed balance sheets. Realized gains and losses on sales of investments, if any, are reflected in non-operating income (expense) in the condensed statements of operations.

As of September 30, 2018 and December 31, 2017, the Company had $102.2 million and $100.9 million in short-term available-for-sale investment securities, respectively. During the nine months ended September 30, 2018, these investments earned interest income at a weighted-average fixed rate of approximately 1.5%. For the three and nine months ended September 30, 2018, an unrealized loss of $7 thousand and an unrealized gain of $70 thousand, net of deferred taxes of $5 thousand and $21 thousand, respectively, was recorded within accumulated other comprehensive income ("AOCI") related to these investment securities. For the three and nine months ended September 30, 2017, an unrealized gain of $13 thousand and an unrealized loss of $11 thousand, net of deferred taxes of $7 thousand and $6 thousand, respectively, was recorded within AOCI related to these investment securities. The Company has not recognized any realized gains or losses related to these securities as the Company has not transacted any sale of these securities. As of September 30, 2018 and December 31, 2017, $34 thousand and $105 thousand, net of tax, respectively, remained in AOCI, related to these instruments.

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Accrued Liabilities

9 Months Ended

Sep. 30, 2018

Payables and Accruals [Abstract]

Accrued Liabilities

Accrued Liabilities

Other current liabilities as of September 30, 2018 and December 31, 2017 consist of the following:

	September 30, 2018		December 31, 2017
	(in thousands)
Salaries and wages	$	81,278	$	54,338
Federal excise and other passenger taxes and fees payable	55,743		42,036
Airport obligations	47,476		56,299
Aircraft maintenance	26,438		33,033
Fuel	21,637		25,171
Interest payable	18,965		11,384
Aircraft and facility lease obligations	12,236		16,992
Other	23,369		23,117
Other current liabilities	$	287,142	$	262,370

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Financial Instruments and Risk Management

9 Months Ended

Sep. 30, 2018

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Financial Instruments and Risk Management

Financial Instruments and Risk Management

As part of the Company’s risk management program, the Company from time to time uses a variety of financial instruments to reduce its exposure to fluctuations in the price of jet fuel and interest rates. The Company does not hold or issue derivative financial instruments for trading purposes.

The Company is exposed to credit losses in the event of nonperformance by counterparties to these financial instruments. The Company periodically reviews and seeks to mitigate exposure to the financial deterioration and nonperformance of any counterparty by monitoring the absolute exposure levels, each counterparty's credit ratings and the historical performance of the counterparties relating to hedge transactions. The credit exposure related to these financial instruments is limited to the fair value of contracts in a net receivable position at the reporting date. The Company also maintains security agreements that require the Company to post collateral if the value of selected instruments falls below specified mark-to-market thresholds. The Company records financial derivative instruments at fair value, which includes an evaluation of each counterparty's credit risk. As of September 30, 2018, the Company did not hold any derivatives with requirements to post collateral.

Fuel Derivative Instruments

From time to time, the Company may enter into fuel derivative contracts in order to mitigate the risk of future volatility in fuel prices. The Company's fuel derivative contracts, if any, generally consist of United States Gulf Coast jet fuel swaps ("jet fuel swaps") and United States Gulf Coast jet fuel options ("jet fuel options"). Both jet fuel swaps and jet fuel options are used at times to protect the refining price risk between the price of crude oil and the price of refined jet fuel, and to manage the risk of increasing fuel prices. Fair value of the instruments is determined using standard option valuation models.

The Company accounts for any fuel derivative contracts at fair value and recognizes them in the balance sheet in prepaid expenses and other current assets or other current liabilities. The Company did not enter into any fuel derivative instruments during the nine months ended September 30, 2018 and 2017 and did not have any outstanding fuel derivatives as of September 30, 2018 and December 31, 2017. Historically, the Company has not elected hedge accounting on any fuel derivative instruments entered into and, as a result, changes in the fair value of fuel derivative contracts, if any, were recorded in aircraft fuel expense.

Interest Rate Swaps

From time to time, the Company may enter into interest rate swaps to fix the benchmark interest rate component of interest payments or for other reasons. These instruments limit the Company's exposure to changes in the benchmark interest rate in the period from the trade date through the date of maturity. Interest rate swaps may be designated as cash flow hedges. The Company generally accounts for interest rate swaps at fair value and recognizes them in the balance sheet in prepaid expenses and other current assets or other current liabilities with changes in fair value recorded within AOCI. As of September 30, 2018 and December 31, 2017, the Company did not have any outstanding interest rate swaps.

Realized gains and losses from cash flow hedges are recorded in the statement of cash flows as a component of cash flows from operating activities. Subsequent to the issuance of each debt instrument, amounts remaining in AOCI are amortized over the life of the fixed-rate debt instrument. During the nine months ended September 30, 2018 and 2017, there were no unrealized gains or losses recorded within AOCI related to these instruments as they settled in 2015. For the three and nine months ended September 30, 2018, the Company reclassified interest rate swap losses of $52 thousand and $172 thousand, net of tax of $27 thousand and $66 thousand, respectively, into earnings. For the three and nine months ended September 30, 2017, the Company reclassified interest rate swap losses of $53 thousand and $160 thousand, net of tax of $31 thousand and $92 thousand, respectively, into earnings. As of September 30, 2018 and December 31, 2017, $1.2 million and $1.4 million, net of tax, respectively, remained in AOCI, related to these instruments.

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Commitments and Contingencies

9 Months Ended

Sep. 30, 2018

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

Commitments and Contingencies

Aircraft-Related Commitments and Financing Arrangements

The Company’s contractual purchase commitments consist primarily of aircraft and engine acquisitions through manufacturers. During the first quarter of 2018, the Company negotiated revisions to its A320 aircraft order. The Company originally had 14 A320neo aircraft scheduled for delivery in 2019. Pursuant to the revisions, 5 of the 14 scheduled A320neo aircraft were converted to A320ceo aircraft and are scheduled to be delivered in the remainder of 2018 and 2019. During the third quarter of 2018, the Company entered into operating lease agreements for the lease of seven A320neos that are scheduled to be delivered in the remainder of 2018 and 2019. As of September 30, 2018, the Company's aircraft orders consisted of the following:

	Airbus		Third-Party Lessor
	A320ceo	A320neo	A320neo	Total
remainder of 2018	5		3	8
2019	2	9	4	15
2020		16		16
2021		18		18
	7	43	7	57

During the first quarter of 2018, the Company entered into an aircraft purchase agreement for the purchase of 14 A319 aircraft, which were previously financed under operating lease agreements. The contract was deemed a lease modification which resulted in a change of classification from operating leases to capital leases for the 14 aircraft. As a result, the Company recorded a short-term capital lease asset of $236.7 million within flight equipment and a short-term capital lease obligation of $143.8 million, net of the related maintenance reserves and security deposits, within current maturities of long-term debt and capital leases on the condensed balance sheet as of March 31, 2018. The purchase of all 14 aircraft was completed during the second quarter of 2018 for an aggregate gross purchase price of $285.0 million, which was comprised of cash payments, net of the application of cash maintenance and security deposits held by the previous lessor. For additional information, refer to Note 5, Special Charges.

During the first quarter of 2018, the Company entered into an agreement to purchase six new engines. As of September 30, 2018, the Company had purchased all six engines, unencumbered. In addition, during the second quarter of 2018, the Company sold 5 used engines for $9.5 million at a loss of $4.4 million which is recorded within loss on disposal of assets in the statement of operations. The Company also has two spare engine orders for V2500 SelectTwo engines with International Aero Engines ("IAE") and nine spare engine orders for PurePower PW1100G-JM engines with Pratt & Whitney. Spare engines are scheduled for delivery from 2018 through 2023. Purchase commitments for these aircraft and engines, including estimated amounts for contractual price escalations and pre-delivery payments, are expected to be $210.2 million for the remainder of 2018, $592.1 million in 2019, $810.8 million in 2020, $775.4 million in 2021, $17.0 million in 2022, and $8.0 million in 2023 and beyond. As of September 30, 2018, the Company had secured debt financing commitments of $39.1 million for 1 aircraft, delivered in October 2018. In addition, the Company has secured financing for seven aircraft to be leased directly from a third-party lessor, scheduled for delivery in 2018 through 2019. Aircraft rent commitments for these 7 leased aircraft are expected to be approximately $1.0 million for the remainder of 2018, $27.2 million in 2019, $29.4 million in 2020, $29.4 million in 2021, $29.4 million in 2022, and $235.9 million in 2023 and beyond. As of September 30, 2018, the Company does not have financing commitments in place for the remaining 49 Airbus aircraft currently on firm order, which are scheduled for delivery in 2018 through 2021.

Interest commitments related to the secured debt financing of 55 delivered aircraft as of September 30, 2018 are $21.6 million for the remainder of 2018, $76.3 million in 2019, $69.7 million in 2020, $63.2 million in 2021, $56.8 million in 2022, and $179.4 million in 2023 and beyond. For principal commitments related to these financed aircraft, refer to Note 12, Debt and Other Obligations. As of September 30, 2018, principal and interest commitments related to the Company's future secured debt financing of 1 undelivered aircraft under the Series 2017-1 EETC are $0 for the remainder of 2018, $4.4 million in 2019, $4.0 million in 2020, $3.3 million in 2021, $3.1 million in 2022, and $34.0 million in 2023 and beyond.

As of September 30, 2018, the Company had a fleet consisting of 121 A320 family aircraft. As of September 30, 2018, this fleet was comprised of 44 aircraft financed under operating leases, with lease term expirations between 2021 and 2029, and 77 purchased aircraft, of which 22 were purchased off lease and are currently unencumbered. In addition, as of September 30, 2018, the Company had 12 spare engines financed under operating leases with lease term expiration dates ranging from 2019 to 2027, and owned 6 unencumbered spare engines of which 1 was purchased off lease. One of the Company's leased aircraft has variable rent payments, which fluctuate based on changes in London Interbank Offered Rate ("LIBOR"). The Company entered into sale leaseback transactions with third-party aircraft lessors for some of these aircraft and engine leases. Deferred losses resulting from these sale leaseback transactions are included in other long-term assets on the accompanying balance sheet. Deferred losses are recognized as an increase to rent expense on a straight-line basis over the term of the respective operating leases. Deferred gains are included in deferred gains and other long-term liabilities on the accompanying balance sheet. Deferred gains are recognized as a decrease to rent expense on a straight-line basis over the term of the respective operating leases.

Under the terms of the lease agreements, the Company will continue to operate and maintain the aircraft. Payments under the majority of the lease agreements are fixed for the term of the lease. The lease agreements contain standard termination events, including termination upon a breach of the Company's obligations to make rental payments and upon any other material breach of the Company's obligations under the leases, and standard maintenance and return condition provisions. These return provisions are evaluated at inception of the lease and throughout the lease terms and are accounted for as supplemental rent expense when it is probable that such amounts will be incurred. Upon a termination of the lease due to a breach by the Company, the Company would be liable for standard contractual damages, possibly including damages suffered by the lessor in connection with remarketing the aircraft or while the aircraft is not leased to another party.

In July 2015, the Company executed an upgrade service agreement with Airbus Americas Customer Services Inc. ("Airbus") to reconfigure the seating and increase capacity in 40 of the Company’s A320ceos from 178 to 182 seats ("reconfiguration"). The reconfiguration of the aircraft commenced in the first quarter of 2016 and was completed in the second quarter of 2018. As of September 30, 2018, the Company had no further commitments related to this agreement. The amounts related to the reconfiguration are capitalized within flight equipment on the balance sheet.

Future minimum lease payments under capital leases and noncancellable operating leases at September 30, 2018 were as follows: 

		Capital Leases		Aircraft and Spare Engine Operating Leases		Property Facility Operating Leases		Total Operating and Capital Lease Obligations
	(in thousands)
remainder of 2018		$	165	$	42,762	$	15,122	$	58,049
2019		625		167,360		45,018		213,003
2020		249		161,876		29,636		191,761
2021		28		160,185		16,645		176,858
2022		—		146,904		14,403		161,307
2023 and thereafter		—		419,925		101,897		521,822
Total minimum lease payments		$	1,067	$	1,099,012	$	222,721	$	1,322,800
Less amount representing interest		49
Present value of minimum lease payments		$	1,018
Less current portion		596
Long-term portion		$	422

The majority of the Company's capital lease obligations relate to the lease of computer equipment used by the Company's flight crew. Payments related to the lease of computer equipment are fixed for the 3-year term of the lease.

Aircraft rent expense consists of monthly lease rents for aircraft and spare engines under the terms of the Company's aircraft and spare engine lease agreements recognized on a straight-line basis. Aircraft rent expense also includes supplemental rent. Supplemental rent is made up of maintenance reserves paid or expected to be paid to aircraft lessors in advance of the performance of major maintenance activities that are not probable of being reimbursed, and probable and estimable return condition obligations. The Company expects supplemental rent to increase as individual aircraft lease agreements approach their respective termination dates and the Company begins to accrue the estimated cost of return conditions for the corresponding aircraft.

Some of the Company’s aircraft and engine master lease agreements provide that the Company pays maintenance reserves to aircraft lessors to be held as collateral in advance of the Company’s required performance of major maintenance activities. A majority of these maintenance reserve payments are calculated based on a utilization measure, such as flight hours or cycles, while some maintenance reserve payments are fixed, time-based contractual amounts. Fixed maintenance reserve payments for these aircraft and related flight equipment, including estimated amounts for contractual price escalations, are expected to be $1.8 million for the remainder of 2018, $5.8 million in 2019, $5.6 million in 2020, $5.7 million in 2021, $4.9 million in 2022, and $12.9 million in 2023 and beyond. These lease agreements generally provide that maintenance reserves are reimbursable to the Company upon completion of the maintenance event. Some of the master lease agreements do not require that the Company pay maintenance reserves so long as the Company's cash balance does not fall below a certain level. As of September 30, 2018, the Company is in full compliance with those requirements and does not anticipate having to pay reserves related to these master leases in the future.

The Company is contractually obligated to pay the following minimum guaranteed payments for its reservation system and other miscellaneous subscriptions and services as of September 30, 2018: $2.5 million for the remainder of 2018, $12.6 million in 2019, $12.7 million in 2020, $9.9 million in 2021, $10.0 million in 2022, and $66.6 million thereafter. During the first quarter of 2018, the Company entered into a contract renewal with its reservation system provider which expires in 2028.

Litigation

The Company is subject to commercial litigation claims and to administrative and regulatory proceedings and reviews that may be asserted or maintained from time to time. The Company believes the ultimate outcome of such lawsuits, proceedings and reviews will not, individually or in the aggregate, have a material adverse effect on its financial position, liquidity or results of operations.

Credit Card Processing Arrangements

The Company has agreements with organizations that process credit card transactions arising from the purchase of air travel, baggage charges, and other ancillary services by customers. As is standard in the airline industry, the Company's contractual arrangements with credit card processors permit them, under certain circumstances, to retain a holdback or other collateral, which the Company records as restricted cash, when future air travel and other future services are purchased via credit card transactions. The required holdback is the percentage of the Company's overall credit card sales that its credit card processors hold to cover refunds to customers if the Company fails to fulfill its flight obligations.

The Company's credit card processors do not require the Company to maintain cash collateral provided that the Company satisfies certain liquidity and other financial covenants. Failure to meet these covenants would provide the processors the right to place a holdback resulting in a commensurate reduction of unrestricted cash. As of September 30, 2018 and December 31, 2017, the Company was in compliance with such liquidity and other financial covenants in its credit card processing agreements and the processors were holding back no remittances.

The maximum potential exposure to cash holdbacks by the Company's credit card processors, based upon advance ticket sales and $9 Fare Club memberships as of September 30, 2018 and December 31, 2017, was $341.5 million and $286.3 million, respectively.

Employees

The Company has 4 union-represented employee groups that together represented approximately 76% of all employees at September 30, 2018. The table below sets forth the Company's employee groups and status of the collective bargaining agreements as of September 30, 2018.

Employee Groups	Representative	Amendable Date	Percentage of Workforce
Pilots	Air Line Pilots Association, International ("ALPA")	February 2023	27%
Flight Attendants	Association of Flight Attendants ("AFA-CWA")	May 2021	44%
Dispatchers	Professional Airline Flight Control Association ("PAFCA")	October 2023	1%
Ramp Service Agents	International Association of Machinists and Aerospace Workers ("IAMAW")	June 2020	4%

In August 2015, the Company's collective bargaining agreement with its pilots, represented by ALPA, became amendable. In June 2016, ALPA requested the services of the National Mediation Board ("NMB") to facilitate negotiations for an amended agreement and the Company joined ALPA in the request. In January 2018, under the guidance of the NMB assigned mediators, the parties reached a tentative agreement. In February 2018, the pilot group voted to approve the new five-year agreement with the Company. The new agreement includes a one-time ratification incentive and other negotiated contractual provisions which were recorded in special charges (credits) within operating expenses in the condensed statement of operations for the nine months ended September 30, 2018. For additional information, refer to Note 5, Special Charges.

In December 2017, the Professional Airline Flight Control Association ("PAFCA") filed an application with the NMB seeking to represent the Company's dispatchers, who were previously represented by the Transport Workers Union ("TWU"). In January 2018, the NMB determined that a representation election would be held. The voting period for the representation election took place through February 20, 2018 and the dispatchers elected to be represented by the PAFCA. In June 2018, the Company commenced negotiations with PAFCA for an amended agreement with its dispatchers. In October 2018, PAFCA and the Company reached a tentative agreement for a new five-year agreement, which was ratified by the PAFCA members on October 17, 2018. The terms of the new agreement are currently in effect.

In June 2018, the NMB notified the Company that the TWU filed an application seeking a representation election for the Company's passenger service agents. The NMB determined that a representation election would be held and the voting period for the election took place through September 4, 2018. The Company’s passenger service agents voted to be represented by the TWU, but the representation applies only to the Company’s Fort Lauderdale station where the Company has direct employees in the passenger service classification. The Company and the TWU will meet in late October 2018 to begin negotiating a collective bargaining agreement.

The Company is self-insured for health care claims, up to a stop loss amount for eligible participating employees and qualified dependent medical claims, subject to deductibles and limitations. The Company’s liabilities for claims incurred but not reported are determined based on an estimate of the ultimate aggregate liability for claims incurred. The estimate is

calculated from actual claim rates and adjusted periodically as necessary. The Company has accrued $5.6 million and $3.9 million in health care claims as of September 30, 2018 and December 31, 2017, respectively.

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Fair Value Measurements

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

Fair Value Measurements

Fair Value Measurements

Under ASC 820, "Fair Value Measurements and Disclosures", disclosures relating to how fair value is determined for assets and liabilities are required, and a hierarchy for which these assets and liabilities must be grouped is established, based on significant levels of inputs, as follows:

Level 1—Quoted prices in active markets for identical assets or liabilities.

Level 2—Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The Company utilizes several valuation techniques in order to assess the fair value of the Company’s financial assets and liabilities.

Fuel Derivative Instruments

From time to time, the Company may enter into fuel derivative contracts in order to mitigate the risk of future volatility in fuel prices. The Company’s fuel derivative contracts generally consist of jet fuel swaps and jet fuel options. These instruments are valued using energy and commodity market data, which is derived by combining raw inputs with quantitative models and processes to generate forward curves and volatilities.

The Company utilizes the market approach to measure fair value for its fuel derivative instruments, if any. The market approach uses prices and other relevant information generated by market transactions involving identical or comparable assets or liabilities.

The Company has not historically elected hedge accounting on its fuel derivative instruments, if any. As a result, the Company would record the fair value adjustment of any fuel derivatives in the accompanying statement of operations within aircraft fuel and on the balance sheet within prepaid expenses and other current assets or other current liabilities, depending on whether the net fair value of the derivatives is in an asset or liability position as of the respective date. Fair values of any fuel derivative instruments are determined using standard option valuation models. The Company also considers counterparty risk and its own credit risk in its determination of all estimated fair values. The Company offsets fair value amounts recognized for any derivative instruments executed with the same counterparty under a master netting arrangement. The Company determines fair value of any jet fuel options utilizing an option pricing model based on inputs that are either readily available in public markets or can be derived from information available in publicly quoted markets. The Company has consistently applied these valuation techniques in all periods presented and believes it has obtained the most accurate information available for the types of derivative contracts it holds.

The fair value of the Company's jet fuel swaps, if any, are determined based on inputs that are readily available in public markets or can be derived from information available in publicly quoted markets; therefore, the Company categorizes these instruments as Level 2. Due to the fact that certain inputs utilized to determine the fair value of jet fuel options are unobservable (principally implied volatility), the Company categorizes these derivatives as Level 3. Implied volatility of a jet fuel option is the volatility of the price of the underlying commodity that is implied by the market price of the option based on an option pricing model. Thus, it is the volatility that when used in a particular pricing model yields a theoretical value for the option equal to the current market price of that option. Implied volatility, a forward-looking measure, differs from historical volatility because the latter is calculated from known past returns. At each balance sheet date, the Company substantiates and adjusts unobservable inputs. The Company routinely assesses the valuation model's sensitivity to changes in implied volatility. As of September 30, 2018 and December 31, 2017, the Company had no outstanding jet fuel derivatives.

Long-Term Debt

The estimated fair value of the Company's term loan debt agreements has been determined to be Level 3 as certain inputs used to determine the fair value of these agreements are unobservable. The Company utilizes a discounted cash flow method to estimate the fair value of the Level 3 long-term debt. The estimated fair value of the Company's publicly and non-

publicly held EETC debt agreements has been determined to be Level 2 as the Company utilizes quoted market prices in markets with low trading volumes to estimate the fair value of its Level 2 long-term debt.

The carrying amounts and estimated fair values of the Company's long-term debt at September 30, 2018 and December 31, 2017 were as follows:

	September 30, 2018				December 31, 2017				Fair Value Level Hierarchy
	Carrying Value		Estimated Fair Value		Carrying Value		Estimated Fair Value
	(in millions)
Senior term loans	$	391.4	$	395.5	$	417.9	$	435.3	Level 3
Junior term loans	33.2		33.6		39.3		40.4		Level 3
Fixed-rate loans	493.9		487.2		518.0		528.6		Level 3
2015-1 EETC Class A	393.6		389.8		408.6		420.9		Level 2
2015-1 EETC Class B	84.0		83.5		92.0		94.2		Level 2
2015-1 EETC Class C	115.2		114.4		—		—		Level 2
2017-1 EETC Class AA	223.3		213.6		37.5		37.4		Level 2
2017-1 EETC Class A	74.4		71.1		12.5		12.6		Level 2
2017-1 EETC Class B	76.7		73.3		13.8		13.8		Level 2
2017-1 EETC Class C	78.9		78.3		—		—		Level 2
Total long-term debt	$	1,964.6	$	1,940.3	$	1,539.6	$	1,583.2

Cash and Cash Equivalents

Cash and cash equivalents at September 30, 2018 and December 31, 2017 are comprised of liquid money market funds and cash, and are categorized as Level 1 instruments. The Company maintains cash with various high-quality financial institutions.

Short-term Investment Securities

Short-term investment securities at September 30, 2018 and December 31, 2017 are classified as available-for-sale and consist of U.S. Treasury and U.S. government agency securities with contractual maturities of 12 months or less. The Company's short-term investment securities are categorized as Level 1 instruments, as the Company uses quoted market prices in active markets when determining the fair value of these securities. For additional information, refer to Note 7, Short-term Investment Securities.

Assets and liabilities measured at gross fair value on a recurring basis are summarized below:

	Fair Value Measurements as of September 30, 2018
	Total		Level 1		Level 2		Level 3
	(in millions)
Cash and cash equivalents	$	773.7	$	773.7	$	—	$	—
Short-term investment securities	102.2		102.2		—		—
Total assets	$	875.9	$	875.9	$	—	$	—
Total liabilities	$	—	$	—	$	—	$	—

	Fair Value Measurements as of December 31, 2017
	Total		Level 1		Level 2		Level 3
	(in millions)
Cash and cash equivalents	$	800.8	$	800.8	$	—	$	—
Short-term investment securities	100.9		100.9		—		—
Total assets	$	901.7	$	901.7	$	—	$	—
Total liabilities	$	—	$	—	$	—	$	—

The Company had no transfers of assets or liabilities between any of the above levels during the periods ended September 30, 2018 and December 31, 2017.

The Company's Valuation Group, which reports to the Chief Financial Officer, is made up of individuals from the Company's Treasury and Corporate Accounting departments. The Valuation Group is responsible for the execution of the Company's valuation policies and procedures. The Valuation Group compares the results of the Company's internally developed valuation methods with counterparty reports at each balance sheet date, assesses the Company's valuation methods for accurateness and identifies any needs for modification.

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Debt and Other Obligations

9 Months Ended

Sep. 30, 2018

Debt Disclosure [Abstract]

Debt and Other Obligations

Debt and Other Obligations

As of September 30, 2018, the Company had outstanding non-public and public debt instruments. During the nine months ended September 30, 2018, the Company issued additional debt through the 2015-1 and 2017-1 EETCs described below.

2017-1 Class AA, Class A and Class B EETCs

In November 2017, the Company created three separate pass-through trusts, which issued $420.5 million aggregate face amount of Series 2017-1 Class AA, Class A and Class B EETCs in connection with the financing of 7 new Airbus A320 aircraft and 5 new Airbus A321 aircraft. Each class of certificates represents a fractional undivided interest in the respective pass-through trusts and is not an obligation of the Company. The proceeds from the issuance of these certificates are initially held in escrow by a depositary and, upon satisfaction of certain terms and conditions, are released and used to purchase equipment notes which are issued by the Company and secured by the Company's aircraft. Interest on the issued and outstanding equipment notes is payable semiannually on February 15 and August 15 of each year, commencing on August 15, 2018, and principal on such equipment notes is scheduled for payment on February 15 and August 15 of certain years. Principal payments commenced on August 15, 2018 in the case of five new Airbus A321 aircraft delivered from February 2018 to March 2018 and three Airbus A320 aircraft delivered from December 2017 to January 2018 and will commence on February 15, 2019 for three Airbus A320 aircraft delivered from April 2018 to August 2018 and one Airbus A320 aircraft scheduled for delivery in October 2018. Issued and outstanding Series AA and Series A equipment notes mature in February 2030 and Series B equipment notes mature in February 2026. Issued and outstanding Series AA, Series A and Series B equipment notes accrue interest at a rate of 3.375%, 3.650% and 3.800%, respectively. As of September 30, 2018, $388.0 million of the proceeds from the sale of the Series 2017-1 Class AA, Class A and Class B EETCs had been used to purchase equipment notes in connection with the financing of five Airbus A321 aircraft and six Airbus A320 aircraft. The remaining $32.5 million of escrowed proceeds held by the pass-through trusts will be used to purchase equipment notes as the remaining one new aircraft is delivered in October 2018. Equipment notes that are issued are reported as debt on the Company's condensed balance sheets.

2015-1C and 2017-1C EETCs

In May 2018, the Company completed a private placement of an aggregate amount of $115.2 million pass-through certificates, Series 2015-1C. The Company entered into 15 separate participation agreement amendments to existing participation agreements that were entered into by the Company during the period from October 2015 to February 2017 under the existing pass through trust formed by the Company on August 11, 2015. The Series 2015-1C equipment notes are secured by 12 Airbus A321 aircraft previously delivered from October 2015 to January 2017 and 3 Airbus A320 aircraft previously delivered from March 2016 to June 2016. The Series 2015-1C equipment notes mature in April 2023 and accrue interest at a

rate of 4.93%. Principal and interest on the issued and outstanding Series 2015-1C equipment notes is payable semiannually on April 1 and October 1 of each year, commencing on October 1, 2018. Equipment notes that are issued are reported as debt on the Company's condensed balance sheets.

In May 2018, the Company also completed a private placement of an aggregate amount of $85.5 million pass-through certificates, Series 2017-1C. The Company entered into 9 separate participation agreement amendments to existing participation agreements that were entered into by the Company during the period from December 2017 to April 2018 under the existing pass through trust formed by the Company on November 28, 2017. The participation agreement amendments provide for the issuance of series 2017-1C equipment notes, in the aggregate principal amount of $65.7 million in connection with previously delivered aircraft. The 2017-1C equipment notes are secured by five Airbus A321 aircraft previously delivered from February 2018 to March 2018 and four Airbus A320 aircraft previously delivered from December 2017 to April 2018. The Series 2017-1C equipment notes mature in February 2023 and accrue interest at a rate of 5.11%. Interest on the Class C 2017-1 issued and outstanding equipment notes are payable semiannually on February 15 and August 15 of each year, commencing on August 15, 2018. The entire principal on the issued and outstanding Series 2017-1C equipment notes is scheduled for payment on February 15, 2023. As of September 30, 2018, $13.2 million of the proceeds from the sale of the Series 2017-1 Class C had been used to purchase equipment notes in connection with the financing of two Airbus A320 aircraft. The remaining $6.6 million of escrowed proceeds held by the pass-through trusts will be used to purchase equipment notes when the remaining 1 Airbus A320 aircraft is delivered in October 2018. Equipment notes that are issued are reported as debt on the Company's condensed balance sheets.

The Company evaluated whether the pass-through trusts formed are variable interest entities ("VIEs") required to be consolidated by the Company under applicable accounting guidance. The Company determined that the pass-through trusts are VIEs and that it does not have a variable interest in the pass-through trusts. Based on this analysis, the Company determined that it is not required to consolidate these pass-through trusts.

Long-term debt is comprised of the following:

	As of				Three Months Ended September 30,				Nine Months Ended September 30,
	September 30, 2018		December 31, 2017		2018		2017		2018		2017
	(in millions)				(weighted-average interest rates)
Fixed-rate senior term loans due through 2027	$	391.4	$	417.9	4.10	%	4.10	%	4.10	%	4.10	%
Fixed-rate junior term loans due through 2022	33.2		39.3		6.90	%	6.90	%	6.90	%	6.90	%
Fixed-rate loans due through 2029	493.9		518.0		3.83	%	3.76	%	3.83	%	3.76	%
Fixed-rate class A 2015-1 EETC due through 2028	393.6		408.6		4.10	%	4.10	%	4.10	%	4.10	%
Fixed-rate class B 2015-1 EETC due through 2024	84.0		92.0		4.45	%	4.45	%	4.45	%	4.45	%
Fixed-rate class C 2015-1 EETC due through 2023	115.2		—		4.93	%	N/A		4.93	%	N/A
Fixed-rate class AA 2017-1 EETC due through 2030	223.3		37.5		3.38	%	N/A		3.38	%	N/A
Fixed-rate class A 2017-1 EETC due through 2030	74.4		12.5		3.65	%	N/A		3.65	%	N/A
Fixed-rate class B 2017-1 EETC due through 2026	76.7		13.8		3.80	%	N/A		3.80	%	N/A
Fixed-rate class C 2017-1 EETC due through 2023	78.9		—		5.11	%	N/A		5.11	%	N/A
Long-term debt	1,964.6		1,539.6
Less current maturities	150.2		115.4
Less unamortized discounts	43.9		36.7
Total	$	1,770.5	$	1,387.5

During the three and nine months ended September 30, 2018, the Company made scheduled principal payments of $32.6 million and $93.2 million on its outstanding debt obligations, respectively. During the three and nine months ended September 30, 2017, the Company made scheduled principal payments of $13.4 million and $63.4 million on its outstanding debt obligations, respectively.

At September 30, 2018, long-term debt principal payments for the next five years and thereafter are as follows:

	September 30, 2018
	(in millions)
remainder of 2018	$	44.0
2019	158.3
2020	155.3
2021	151.0
2022	147.9
2023 and beyond	1,308.1
Total debt principal payments	$	1,964.6

Interest Expense

Interest expense related to long-term debt consisted of the following:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
	(in thousands)
Senior term loans	$	4,195	$	4,564	$	12,769	$	13,854
Junior term loans	605		746		1,908		2,323
Fixed-rate loans	4,844		2,811		14,636		4,555
Class A 2015-1 EETC	4,057		4,366		12,214		12,995
Class B 2015-1 EETC	939		1,118		2,881		3,410
Class C 2015-1 EETC	1,420		—		2,209		—
Class AA 2017-1 EETC	1,751		—		4,008		—
Class A 2017-1 EETC	631		—		1,445		—
Class B 2017-1 EETC	700		—		1,636		—
Class C 2017-1 EETC	934		—		1,400		—
Commitment fees	50		29		153		87
Amortization of debt discounts	1,784		1,362		4,930		3,883
Total	$	21,910	$	14,996	$	60,189	$	41,107

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Subsequent Event

9 Months Ended

Sep. 30, 2018

Subsequent Events [Abstract]

Subsequent Events

Subsequent EventsOn October 23, 2018, the Company entered into a revolving credit facility for up to $160 million secured by the collateral assignment of certain of the Company's rights under the Company's purchase agreement with Airbus, related to 43 Airbus A320neo aircraft scheduled to be delivered between August 2019 and December 2021. The Company intends to use any proceeds for working capital, capital expenditures and other general corporate purposes. The final maturity of the facility is December 30, 2020. As of October 24, 2018, no amounts have been drawn. Any drawdowns on the facility are subject to certain terms and conditions.

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Basis of Presentation (Policies)

9 Months Ended

Sep. 30, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Basis of accounting

The accompanying unaudited condensed financial statements include the accounts of Spirit Airlines, Inc. ("the Company"). These unaudited condensed financial statements reflect all normal recurring adjustments which management believes are necessary to fairly present the financial position, results of operations and cash flows of the Company for the respective periods presented. Certain information and footnote disclosures normally included in the annual financial statements prepared in accordance with U.S. generally accepted accounting principles ("GAAP") have been condensed or omitted pursuant to the rules and regulations of the Securities and Exchange Commission for Form 10-Q. These unaudited interim condensed financial statements should be read in conjunction with the audited financial statements of the Company and notes thereto included in the Company's Annual Report on Form 10-K for the year ended December 31, 2017 filed with the Securities and Exchange Commission on February 13, 2018.

Use of estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect both the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from these estimates.

Recent Accounting Developments

Recently Adopted Accounting Pronouncements

Revenue from Contracts with Customers

In May 2014, the Financial Accounting Standards Board ("the FASB") issued Accounting Standards Update ("ASU") No. 2014-09, ("ASU 2014-09") "Revenue from Contracts with Customers." The objective of ASU 2014-09 is to establish a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers. The Company adopted this guidance on January 1, 2018 utilizing the full retrospective method of adoption allowed by the standard, in order to provide for comparative results in all periods presented. The most significant impact of this ASU is the elimination of the incremental cost method for frequent flier program accounting, which requires the Company to re-value and record a liability associated with customer flight miles earned as part of the Company’s frequent flier program with a relative fair value approach. The classification and timing of recognition of certain ancillary fees is also impacted by the adoption of ASU 2014-09. While the adoption did not have a significant impact on earnings, the classification of certain revenues, such as bags, seats and other travel-related fees are now deemed part of the single performance obligation of providing passenger transportation. Refer to Note 3, Revenue Recognition for information regarding the Company's adoption of ASU 2014-09 and to Note 4, Revenue Disaggregation for the presentation of passenger revenues disaggregated by fare and non-fare.

Financial Instruments

In January 2016, the FASB issued ASU 2016-01, “Financial Instruments – Overall (Subtopic 825-10).” ASU 2016-01 makes several modifications to Subtopic 825-10 including the elimination of the available-for-sale classification of equity investments, and requires equity investments with readily determinable fair values to be measured at fair value with changes in fair value recognized in net income. ASU 2016-01 is effective for the Company for interim and annual periods beginning January 1, 2018. The Company adopted this guidance on January 1, 2018 with no material impact on the financial statements.

Statement of Cash Flows

In August 2016, the FASB issued ASU No. 2016-15, "Statement of Cash Flows." The standard is intended to reduce diversity in practice in how certain transactions are classified in the statement of cash flows. This standard is effective for the

Company for fiscal years, and interim periods within those years, beginning January 1, 2018. The Company adopted this guidance on January 1, 2018 with no material impact on the financial statements.

Recently Issued Accounting Pronouncements Not Yet Adopted

Leases

In February 2016, the FASB issued ASU No. 2016-02, "Leases (Topic 842)." This standard will require all lessees to recognize a right-of-use asset and a lease liability, initially measured at the present value of the lease payments, for all leases with a term greater than 12 months. The standard is effective for the Company effective January 1, 2019. Early adoption is permitted. However, the Company does not plan to early adopt. The Company has established a cross functional project plan and is in the process of testing items necessary to account for the new standard. The Company expects this standard to have a significant impact on its condensed balance sheets due to the recognition of right-of-use assets and lease liabilities for leases. The Company does not expect the adoption to have a significant impact on its lease classification, a material impact on its condensed statement of operations, or a notable impact on its liquidity. Additionally, the Company does not expect the standard to have a material impact on the Company’s debt-covenant compliance under its current agreements. Refer to Note 10, Commitments and Contingencies for information regarding the Company's undiscounted future lease payments and the timing of those payments. 

In July 2018, the FASB issued additional guidance on the accounting for leases. The guidance provides companies with another transition method that allows entities to recognize a cumulative-effect adjustment to the opening balance of retained earnings as of the date of adoption. Under this method, previously presented years’ financial positions and results would not be adjusted. The new guidance also provides lessors with a practical expedient, by class of underlying asset, to not separate non-lease components from the associated lease component if (1) the non-lease components would otherwise be accounted for under the new revenue recognition standard, (2) both the timing and pattern of transfer are the same for the non-lease components and associated lease component, and (3) if accounted for separately, the lease component would be classified as an operating lease. The Company is assessing the use of practical expedients in its accounting for leases.

Accounting for Credit Losses

In June 2016, the FASB issued ASU No. 2016-13, "Financial Instruments - Credit Losses." The standard requires the use of an "expected loss" model on certain types of financial instruments. The standard also amends the impairment model for available-for-sale securities and requires estimated credit losses to be recorded as allowances rather than as reductions to the amortized cost of the securities. This standard is effective for the Company for fiscal years, and interim periods within those years, beginning January 1, 2020, with early adoption permitted. The Company is evaluating the new guidance, but does not expect it to have a material impact on its financial statements.

Income Taxes

In March 2018, the FASB issued ASU 2018-05, Income Taxes ("Topic 740") - Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 118. The standard amends Accounting Standards Codification 740, Income Taxes ("ASC 740") to provide guidance on accounting for the tax effects of the Tax Cuts and Jobs Act (the "Tax Act") pursuant to Staff Accounting Bulletin No. 118. The provisional income tax amounts recorded may be affected as the Company gains a more thorough understanding of the tax law, including those related to the deductibility of acquired assets, state tax treatment and amounts related to employee compensation. The provisional accounting impacts for the Company may change in future reporting periods until the accounting is finalized, which will occur no later than the fourth quarter of 2018. The Company does not expect material changes to the financial statements in the fourth quarter of 2018 as a result of finalizing the accounting for the Tax Act.

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Revenue Recognition (Tables)

9 Months Ended

Sep. 30, 2018

Revenue from Contract with Customer [Abstract]

Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block]

The following tables show adjustments made due to the adoption of ASU 2014-09 on the December 31, 2017 and 2016 statements of operations. Previously reported results were derived from audited financial statements included in Company's Annual Report on Form 10-K for the fiscal years ended December 31, 2017 and December 31, 2016, as applicable.

	Year Ended December 31, 2017
	(in thousands, except share and per share data)
	As Reported			Topic 606 Adjustment			As Adjusted
Operating revenues:
Passenger	$	1,366,034		$	1,206,853		$	2,572,887
Other	1,281,632			(1,210,967		)	70,665
Total operating revenues	2,647,666			(4,114		)	2,643,552
Operating expenses:
Aircraft fuel	615,581			—			615,581
Salaries, wages and benefits	527,959			—			527,959
Aircraft rent	205,852			—			205,852
Landing fees and other rents	180,655			—			180,655
Depreciation and amortization	140,152			—			140,152
Maintenance, materials and repairs	110,439			—			110,439
Distribution	113,620			(148		)	113,472
Special charges	12,629			—			12,629
Loss on disposal of assets	4,168			—			4,168
Other operating	347,820			—			347,820
Total operating expenses	2,258,875			(148		)	2,258,727
Operating income	388,791			(3,966		)	384,825
Other (income) expense:
Interest expense	57,302			—			57,302
Capitalized interest	(13,793		)	—			(13,793		)
Interest income	(8,736		)	—			(8,736		)
Other expense	366			—			366
Total other (income) expense	35,139			—			35,139
Income before income taxes	353,652			(3,966		)	349,686
Provision (benefit) for income taxes	(66,954		)	1,118			(65,836		)
Net income	$	420,606		$	(5,084	)	$	415,522
Basic earnings per share	$	6.08		$	(0.07	)	$	6.00
Diluted earnings per share	$	6.06		$	(0.07	)	$	5.99

	Year Ended December 31, 2016
	(in thousands, except share and per share data)
	As Reported			Topic 606 Adjustment			As Adjusted
Operating revenues:
Passenger	$	1,200,621		$	1,057,180		$	2,257,801
Other	1,121,335			(1,059,115		)	62,220
Total operating revenues	2,321,956			(1,935		)	2,320,021
Operating expenses:
Salaries, wages and benefits	472,471			—			472,471
Aircraft fuel	447,553			—			447,553
Aircraft rent	201,675			—			201,675
Landing fees and other rents	151,679			—			151,679
Depreciation and amortization	101,136			—			101,136
Maintenance, materials and repairs	98,587			—			98,587
Distribution	96,627			268			96,895
Special charges	37,189			—			37,189
Loss on disposal of assets	4,187			—			4,187
Other operating	267,191			—			267,191
Total operating expenses	1,878,295			268			1,878,563
Operating income	443,661			(2,203		)	441,458
Other (income) expense:
Interest expense	41,654			—			41,654
Capitalized interest	(12,705		)	—			(12,705		)
Interest income	(5,276		)	—			(5,276		)
Other expense	528			—			528
Total other (income) expense	24,201			—			24,201
Income before income taxes	419,460			(2,203		)	417,257
Provision (benefit) for income taxes	154,581			(807		)	153,774
Net income	$	264,879		$	(1,396	)	$	263,483
Basic earnings per share	$	3.77		$	(0.02	)	$	3.75
Diluted earnings per share	$	3.76		$	(0.02	)	$	3.74

The following table shows adjusted balances after the adoption of ASU 2014-09 on the quarterly statements of operations for each quarter of 2017.

	For the Quarter Ended
	March 31, 2017			June 30, 2017			September 30, 2017			December 31, 2017
	(in thousands, except share and per share data)
Operating revenues:
Passenger	$	572,287		$	680,880		$	669,072		$	650,647
Other	17,670			19,305			18,155			15,535
Total operating revenues	589,957			700,185			687,227			666,182
Operating expenses:
Aircraft fuel	139,782			142,294			158,300			175,205
Salaries, wages and benefits	127,138			129,892			134,114			136,815
Aircraft rent	57,070			52,566			53,396			42,820
Landing fees and other rents	40,448			45,592			48,498			46,117
Depreciation and amortization	31,509			35,331			36,840			36,472
Maintenance, materials and repairs	26,312			28,985			26,176			28,966
Distribution	25,772			29,835			29,695			28,170
Special charges	4,776			—			7,853			—
Loss on disposal of assets	1,105			1,493			516			1,054
Other operating	77,703			102,885			87,965			79,267
Total operating expenses	531,615			568,873			583,353			574,886
Operating income	58,342			131,312			103,874			91,296
Other (income) expense:
Interest expense	12,473			13,746			15,018			16,065
Capitalized interest	(3,580		)	(3,342		)	(3,203		)	(3,668		)
Interest income	(1,313		)	(1,828		)	(2,605		)	(2,990		)
Other expense	3			104			114			145
Total other (income) expense	7,583			8,680			9,324			9,552
Income before income taxes	50,759			122,632			94,550			81,744
Provision (benefit) for income taxes	19,498			45,391			34,506			(165,231		)
Net income	$	31,261		$	77,241		$	60,044		$	246,975
Basic earnings per share	$	0.45		$	1.11		$	0.87		$	3.59
Diluted earnings per share	$	0.45		$	1.11		$	0.86		$	3.58

The following table shows quarterly adjustments made due to the adoption of ASU 2014-09 on the statements of operations for 2017.

				Adjustments for the Quarter Ended
	Full Year 2017 As Reported			March 31, 2017			June 30, 2017			September 30, 2017			December 31, 2017			Full Year 2017 Adjusted
	(in thousands, except share and per share data)
Operating revenues:
Passenger	$	1,366,034		$	272,525		$	308,959		$	312,865		$	312,504		$	2,572,887
Other	1,281,632			(274,314		)	(310,455		)	(312,869		)	(313,329		)	70,665
Total operating revenues	2,647,666			(1,789		)	(1,496		)	(4		)	(825		)	2,643,552
Operating expenses:
Aircraft fuel	615,581			—			—			—			—			615,581
Salaries, wages and benefits	527,959			—			—			—			—			527,959
Aircraft rent	205,852			—			—			—			—			205,852
Landing fees and other rents	180,655			—			—			—			—			180,655
Depreciation and amortization	140,152			—			—			—			—			140,152
Maintenance, materials and repairs	110,439			—			—			—			—			110,439
Distribution	113,620			(726		)	(73		)	226			425			113,472
Special charges	12,629			—			—			—			—			12,629
Loss on disposal of assets	4,168			—			—			—			—			4,168
Other operating	347,820			—			—			—			—			347,820
Total operating expenses	2,258,875			(726		)	(73		)	226			425			2,258,727
Operating income	388,791			(1,063		)	(1,423		)	(230		)	(1,250		)	384,825
Other (income) expense:
Interest expense	57,302			—			—			—			—			57,302
Capitalized interest	(13,793		)	—			—			—			—			(13,793		)
Interest income	(8,736		)	—			—			—			—			(8,736		)
Other expense	366			—			—			—			—			366
Total other (income) expense	35,139			—			—			—			—			35,139
Income before income taxes	353,652			(1,063		)	(1,423		)	(230		)	(1,250		)	349,686
Provision (benefit) for income taxes	(66,954		)	(389		)	(522		)	(84		)	2,113			(65,836		)
Net income	$	420,606		$	(674	)	$	(901	)	$	(146	)	$	(3,363	)	$	415,522
Basic earnings per share	$	6.08		$	(0.01	)	$	(0.01	)	$	—		$	(0.05	)	$	6.00
Diluted earnings per share	$	6.06		$	(0.01	)	$	(0.01	)	$	—		$	(0.05	)	$	5.99

The following tables show adjustments made due to the adoption of ASU 2014-09 on the December 31, 2017 and 2016 balance sheets. Previously reported results were derived from audited financial statements included in Company's Annual Report on Form 10-K for the fiscal years ended December 31, 2017 and December 31, 2016, as applicable.

	December 31, 2017
	(in thousands)
	As Reported			Topic 606 Adjustment			As Adjusted
Assets
Current assets:
Cash and cash equivalents	$	800,849		$	—		$	800,849
Short-term investment securities	100,937			—			100,937
Accounts receivable, net	49,323			—			49,323
Aircraft maintenance deposits, net	175,615			—			175,615
Income tax receivable	69,844			—			69,844
Prepaid expenses and other current assets	83,692			1,850			85,542
Total current assets	1,280,260			1,850			1,282,110
Property and equipment:
Flight equipment	2,291,110			—			2,291,110
Ground property and equipment	155,166			—			155,166
Less accumulated depreciation	(207,808		)	—			(207,808		)
	2,238,468			—			2,238,468
Deposits on flight equipment purchase contracts	253,687			—			253,687
Long-term aircraft maintenance deposits	150,617			—			150,617
Deferred heavy maintenance, net	99,915			—			99,915
Other long-term assets	121,003			—			121,003
Total assets	$	4,143,950		$	1,850		$	4,145,800
Liabilities and shareholders’ equity
Current liabilities:
Accounts payable	$	22,822		$	—		$	22,822
Air traffic liability	246,404			17,307			263,711
Current maturities of long-term debt	115,430			—			115,430
Other current liabilities	262,370			—			262,370
Total current liabilities	647,026			17,307			664,333
Long-term debt, less current maturities	1,387,498			—			1,387,498
Deferred income taxes	313,140			(4,326		)	308,814
Deferred gains and other long-term liabilities	19,205			3,376			22,581
Shareholders’ equity:
Common stock: Common stock, $0.0001 par value, 240,000,000 shares authorized at December 31, 2017; 69,770,795 issued and 68,196,964 outstanding as of December 31, 2017	7			—			7
Additional paid-in-capital	360,153			—			360,153
Treasury stock, at cost: 1,573,831 shares as of December 31, 2017	(65,854		)	—			(65,854		)
Retained earnings	1,484,239			(14,507		)	1,469,732
Accumulated other comprehensive income (loss)	(1,464		)	—			(1,464		)
Total shareholders’ equity	1,777,081			(14,507		)	1,762,574
Total liabilities and shareholders’ equity	$	4,143,950		$	1,850		$	4,145,800

	December 31, 2016
	(in thousands)
	As Reported			Topic 606 Adjustment			As Adjusted
Assets
Current assets:
Cash and cash equivalents	$	700,900		$	—		$	700,900
Short-term investment securities	100,155			—			100,155
Accounts receivable, net	41,136			—			41,136
Aircraft maintenance deposits, net	87,035			—			87,035
Income tax receivable	—			—			—
Prepaid expenses and other current assets	46,619			1,702			48,321
Total current assets	975,845			1,702			977,547
Property and equipment:
Flight equipment	1,461,525			—			1,461,525
Ground property and equipment	126,206			—			126,206
Less accumulated depreciation	(122,509		)	—			(122,509		)
	1,465,222			—			1,465,222
Deposits on flight equipment purchase contracts	325,688			—			325,688
Long-term aircraft maintenance deposits	199,415			—			199,415
Deferred heavy maintenance, net	75,534			—			75,534
Other long-term assets	110,223			—			110,223
Total assets	$	3,151,927		$	1,702		$	3,153,629
Liabilities and shareholders’ equity
Current liabilities:
Accounts payable	$	15,193		$	—		$	15,193
Air traffic liability	206,392			13,792			220,184
Current maturities of long-term debt	84,354			—			84,354
Other current liabilities	226,011			—			226,011
Total current liabilities	531,950			13,792			545,742
Long-term debt, less current maturities	897,359			—			897,359
Deferred income taxes	308,143			(5,443		)	302,700
Deferred gains and other long-term liabilities	19,868			2,776			22,644
Shareholders’ equity:
Common stock: Common stock, $0.0001 par value, 240,000,000 shares authorized at December 31, 2016; 73,549,872 issued and 69,326,202 outstanding as of December 31, 2016	7			—			7
Additional paid-in-capital	551,004			—			551,004
Treasury stock, at cost: 4,223,670 shares as of December 31, 2016	(218,692		)	—			(218,692		)
Retained earnings	1,063,633			(9,423		)	1,054,210
Accumulated other comprehensive income (loss)	(1,345		)	—			(1,345		)
Total shareholders’ equity	1,394,607			(9,423		)	1,385,184
Total liabilities and shareholders’ equity	$	3,151,927		$	1,702		$	3,153,629

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Revenue Disaggregation (Tables)

9 Months Ended

Sep. 30, 2018

Revenue from Contract with Customer [Abstract]

Schedule of Revenue Disaggregation

The following table shows disaggregated operating revenues for each quarter of 2018 and 2017.

	For the Quarter Ended
	September 30, 2018		June 30, 2018		March 31, 2018		December 31, 2017		September 30, 2017		June 30, 2017		March 31, 2017
	(in thousands)
Operating revenues:
Fare	$	476,660	$	439,549	$	342,695	$	337,324	$	355,593	$	371,443	$	299,035
Non-fare	411,296		396,801		346,446		313,323		313,479		309,437		273,252
Total passenger revenues	887,956		836,350		689,141		650,647		669,072		680,880		572,287
Other revenues	16,374		15,421		14,997		15,535		18,155		19,305		17,670
Total operating revenues	$	904,330	$	851,771	$	704,138	$	666,182	$	687,227	$	700,185	$	589,957

The following table shows disaggregated operating revenues for years ended December 31, 2017 and 2016.    

	Year Ended December 31,
	2017							2016
	(in thousands)
	As Reported		Topic 606 Adjustment			As Adjusted		As Reported		Topic 606 Adjustment			As Adjusted
Operating revenues:
Fare	$	1,366,034	$	(2,639	)	$	1,363,395	$	1,200,621	$	(2,514	)	$	1,198,107
Non-fare	—		1,209,492			1,209,492		—		1,059,694			1,059,694
Total passenger revenues	1,366,034		1,206,853			2,572,887		1,200,621		1,057,180			2,257,801
Other revenues	1,281,632		(1,210,967		)	70,665		1,121,335		(1,059,115		)	62,220
Total operating revenues	$	2,647,666	$	(4,114	)	$	2,643,552	$	2,321,956	$	(1,935	)	$	2,320,021

Operating revenues by geographic region as defined by the Department of Transportation ("DOT") area are summarized below:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
	(in millions)
DOT—Domestic	$	819.3	$	636.3	$	2,236.3	$	1,819.2
DOT—Latin America	85.0		50.9		223.9		158.2
Total	$	904.3	$	687.2	$	2,460.2	$	1,977.4

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Earnings per Share (Tables)

9 Months Ended

Sep. 30, 2018

Earnings Per Share [Abstract]

Computation of basic and diluted earnings per common share

The following table sets forth the computation of basic and diluted earnings per common share:  

	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
	(in thousands, except per share amounts)
Numerator
Net income	$	97,480	$	60,044	$	63,812	$	168,546
Denominator
Weighted-average shares outstanding, basic	68,254		69,370		68,243		69,363
Effect of dilutive stock awards	249		88		103		174
Adjusted weighted-average shares outstanding, diluted	68,503		69,458		68,346		69,537
Net income per share
Basic earnings per common share	$	1.43	$	0.87	$	0.94	$	2.43
Diluted earnings per common share	$	1.42	$	0.86	$	0.93	$	2.42
Anti-dilutive weighted-average shares	5		124		192		76

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Accrued Liabilities (Tables)

9 Months Ended

Sep. 30, 2018

Payables and Accruals [Abstract]

Accrued liabilities included in other current liabilities

Other current liabilities as of September 30, 2018 and December 31, 2017 consist of the following:

	September 30, 2018		December 31, 2017
	(in thousands)
Salaries and wages	$	81,278	$	54,338
Federal excise and other passenger taxes and fees payable	55,743		42,036
Airport obligations	47,476		56,299
Aircraft maintenance	26,438		33,033
Fuel	21,637		25,171
Interest payable	18,965		11,384
Aircraft and facility lease obligations	12,236		16,992
Other	23,369		23,117
Other current liabilities	$	287,142	$	262,370

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Commitments and Contingencies (Tables)

9 Months Ended

Sep. 30, 2018

Commitments and Contingencies Disclosure [Abstract]

Schedule of Future Operating Aircraft Leases

As of September 30, 2018, the Company's aircraft orders consisted of the following:

	Airbus		Third-Party Lessor
	A320ceo	A320neo	A320neo	Total
remainder of 2018	5		3	8
2019	2	9	4	15
2020		16		16
2021		18		18
	7	43	7	57

Future minimum lease payments under noncancelable operating leases

Future minimum lease payments under capital leases and noncancellable operating leases at September 30, 2018 were as follows: 

		Capital Leases		Aircraft and Spare Engine Operating Leases		Property Facility Operating Leases		Total Operating and Capital Lease Obligations
	(in thousands)
remainder of 2018		$	165	$	42,762	$	15,122	$	58,049
2019		625		167,360		45,018		213,003
2020		249		161,876		29,636		191,761
2021		28		160,185		16,645		176,858
2022		—		146,904		14,403		161,307
2023 and thereafter		—		419,925		101,897		521,822
Total minimum lease payments		$	1,067	$	1,099,012	$	222,721	$	1,322,800
Less amount representing interest		49
Present value of minimum lease payments		$	1,018
Less current portion		596
Long-term portion		$	422

Future minimum lease payments under capital leases

Future minimum lease payments under capital leases and noncancellable operating leases at September 30, 2018 were as follows: 

		Capital Leases		Aircraft and Spare Engine Operating Leases		Property Facility Operating Leases		Total Operating and Capital Lease Obligations
	(in thousands)
remainder of 2018		$	165	$	42,762	$	15,122	$	58,049
2019		625		167,360		45,018		213,003
2020		249		161,876		29,636		191,761
2021		28		160,185		16,645		176,858
2022		—		146,904		14,403		161,307
2023 and thereafter		—		419,925		101,897		521,822
Total minimum lease payments		$	1,067	$	1,099,012	$	222,721	$	1,322,800
Less amount representing interest		49
Present value of minimum lease payments		$	1,018
Less current portion		596
Long-term portion		$	422

Employee groups and status of the collective bargaining agreements

The table below sets forth the Company's employee groups and status of the collective bargaining agreements as of September 30, 2018.

Employee Groups	Representative	Amendable Date	Percentage of Workforce
Pilots	Air Line Pilots Association, International ("ALPA")	February 2023	27%
Flight Attendants	Association of Flight Attendants ("AFA-CWA")	May 2021	44%
Dispatchers	Professional Airline Flight Control Association ("PAFCA")	October 2023	1%
Ramp Service Agents	International Association of Machinists and Aerospace Workers ("IAMAW")	June 2020	4%

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Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

Carrying amount and estimated fair value, long-term debt

The carrying amounts and estimated fair values of the Company's long-term debt at September 30, 2018 and December 31, 2017 were as follows:

	September 30, 2018				December 31, 2017				Fair Value Level Hierarchy
	Carrying Value		Estimated Fair Value		Carrying Value		Estimated Fair Value
	(in millions)
Senior term loans	$	391.4	$	395.5	$	417.9	$	435.3	Level 3
Junior term loans	33.2		33.6		39.3		40.4		Level 3
Fixed-rate loans	493.9		487.2		518.0		528.6		Level 3
2015-1 EETC Class A	393.6		389.8		408.6		420.9		Level 2
2015-1 EETC Class B	84.0		83.5		92.0		94.2		Level 2
2015-1 EETC Class C	115.2		114.4		—		—		Level 2
2017-1 EETC Class AA	223.3		213.6		37.5		37.4		Level 2
2017-1 EETC Class A	74.4		71.1		12.5		12.6		Level 2
2017-1 EETC Class B	76.7		73.3		13.8		13.8		Level 2
2017-1 EETC Class C	78.9		78.3		—		—		Level 2
Total long-term debt	$	1,964.6	$	1,940.3	$	1,539.6	$	1,583.2

Schedule of assets and liabilities measured at fair value on a recurring basis

Assets and liabilities measured at gross fair value on a recurring basis are summarized below:

	Fair Value Measurements as of September 30, 2018
	Total		Level 1		Level 2		Level 3
	(in millions)
Cash and cash equivalents	$	773.7	$	773.7	$	—	$	—
Short-term investment securities	102.2		102.2		—		—
Total assets	$	875.9	$	875.9	$	—	$	—
Total liabilities	$	—	$	—	$	—	$	—

	Fair Value Measurements as of December 31, 2017
	Total		Level 1		Level 2		Level 3
	(in millions)
Cash and cash equivalents	$	800.8	$	800.8	$	—	$	—
Short-term investment securities	100.9		100.9		—		—
Total assets	$	901.7	$	901.7	$	—	$	—
Total liabilities	$	—	$	—	$	—	$	—

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Debt and Other Obligations (Tables)

9 Months Ended

Sep. 30, 2018

Debt Disclosure [Abstract]

Schedule of Long-term Debt

Long-term debt is comprised of the following:

	As of				Three Months Ended September 30,				Nine Months Ended September 30,
	September 30, 2018		December 31, 2017		2018		2017		2018		2017
	(in millions)				(weighted-average interest rates)
Fixed-rate senior term loans due through 2027	$	391.4	$	417.9	4.10	%	4.10	%	4.10	%	4.10	%
Fixed-rate junior term loans due through 2022	33.2		39.3		6.90	%	6.90	%	6.90	%	6.90	%
Fixed-rate loans due through 2029	493.9		518.0		3.83	%	3.76	%	3.83	%	3.76	%
Fixed-rate class A 2015-1 EETC due through 2028	393.6		408.6		4.10	%	4.10	%	4.10	%	4.10	%
Fixed-rate class B 2015-1 EETC due through 2024	84.0		92.0		4.45	%	4.45	%	4.45	%	4.45	%
Fixed-rate class C 2015-1 EETC due through 2023	115.2		—		4.93	%	N/A		4.93	%	N/A
Fixed-rate class AA 2017-1 EETC due through 2030	223.3		37.5		3.38	%	N/A		3.38	%	N/A
Fixed-rate class A 2017-1 EETC due through 2030	74.4		12.5		3.65	%	N/A		3.65	%	N/A
Fixed-rate class B 2017-1 EETC due through 2026	76.7		13.8		3.80	%	N/A		3.80	%	N/A
Fixed-rate class C 2017-1 EETC due through 2023	78.9		—		5.11	%	N/A		5.11	%	N/A
Long-term debt	1,964.6		1,539.6
Less current maturities	150.2		115.4
Less unamortized discounts	43.9		36.7
Total	$	1,770.5	$	1,387.5

Schedule of Maturities of Long-term Debt

At September 30, 2018, long-term debt principal payments for the next five years and thereafter are as follows:

	September 30, 2018
	(in millions)
remainder of 2018	$	44.0
2019	158.3
2020	155.3
2021	151.0
2022	147.9
2023 and beyond	1,308.1
Total debt principal payments	$	1,964.6

Schedule of Interest Expense, Long-term Debt

Interest expense related to long-term debt consisted of the following:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
	(in thousands)
Senior term loans	$	4,195	$	4,564	$	12,769	$	13,854
Junior term loans	605		746		1,908		2,323
Fixed-rate loans	4,844		2,811		14,636		4,555
Class A 2015-1 EETC	4,057		4,366		12,214		12,995
Class B 2015-1 EETC	939		1,118		2,881		3,410
Class C 2015-1 EETC	1,420		—		2,209		—
Class AA 2017-1 EETC	1,751		—		4,008		—
Class A 2017-1 EETC	631		—		1,445		—
Class B 2017-1 EETC	700		—		1,636		—
Class C 2017-1 EETC	934		—		1,400		—
Commitment fees	50		29		153		87
Amortization of debt discounts	1,784		1,362		4,930		3,883
Total	$	21,910	$	14,996	$	60,189	$	41,107

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Revenue Recognition - Impact on Statement of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended							9 Months Ended		12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Operating revenues:
Total operating revenues	$ 904,330	$ 851,771	$ 704,138	$ 666,182	$ 687,227	$ 700,185	$ 589,957	$ 2,460,239	$ 1,977,369	$ 2,643,552	$ 2,320,021
Operating expenses:
Aircraft fuel	258,818			175,205	158,300	142,294	139,782	709,644	440,376	615,581	447,553
Salaries, wages and benefits	185,043			136,815	134,114	129,892	127,138	527,895	391,144	527,959	472,471
Aircraft rent	42,682			42,820	53,396	52,566	57,070	134,618	163,032	205,852	201,675
Landing fees and other rents	54,542			46,117	48,498	45,592	40,448	162,774	134,538	180,655	151,679
Depreciation and amortization	43,773			36,472	36,840	35,331	31,509	128,764	103,680	140,152	101,136
Maintenance, materials and repairs	37,778			28,966	26,176	28,985	26,312	99,141	81,473	110,439	98,587
Distribution	37,868			28,170	29,695	29,835	25,772	103,496	85,302	113,472	96,895
Special charges (credits)	(686)			0	7,853	0	4,776	88,656	12,629	12,629	37,189
Loss on disposal of assets	1,069			1,054	516	1,493	1,105	6,561	3,114	4,168	4,187
Other operating	98,318			79,267	87,965	102,885	77,703	283,841	268,553	347,820	267,191
Total operating expenses	759,205			574,886	583,353	568,873	531,615	2,245,390	1,683,841	2,258,727	1,878,563
Operating income	145,125			91,296	103,874	131,312	58,342	214,849	293,528	384,825	441,458
Other (income) expense:
Interest expense	21,925			16,065	15,018	13,746	12,473	60,272	41,237	57,302	41,654
Capitalized interest	(2,657)			(3,668)	(3,203)	(3,342)	(3,580)	(7,205)	(10,125)	(13,793)	(12,705)
Interest income	(4,776)			(2,990)	(2,605)	(1,828)	(1,313)	(13,272)	(5,746)	(8,736)	(5,276)
Other expense	302			145	114	104	3	623	221	366	528
Total other (income) expense	16,538			9,552	9,324	8,680	7,583	130,775	25,587	35,139	24,201
Income before income taxes	128,587			81,744	94,550	122,632	50,759	84,074	267,941	349,686	417,257
Provision (benefit) for income taxes	31,107			(165,231)	34,506	45,391	19,498	20,262	99,395	(65,836)	153,774
Net income	$ 97,480			$ 246,975	$ 60,044	$ 77,241	$ 31,261	$ 63,812	$ 168,546	$ 415,522	$ 263,483
Basic earnings per share	$ 1.43			$ 3.59	$ 0.87	$ 1.11	$ 0.45	$ 0.94	$ 2.43	$ 6.00	$ 3.75
Diluted earnings per share	$ 1.42			$ 3.58	$ 0.86	$ 1.11	$ 0.45	$ 0.93	$ 2.42	$ 5.99	$ 3.74
As Reported [Member]
Operating revenues:
Total operating revenues										$ 2,647,666	$ 2,321,956
Operating expenses:
Aircraft fuel										615,581	447,553
Salaries, wages and benefits										527,959	472,471
Aircraft rent										205,852	201,675
Landing fees and other rents										180,655	151,679
Depreciation and amortization										140,152	101,136
Maintenance, materials and repairs										110,439	98,587
Distribution										113,620	96,627
Special charges (credits)										12,629	37,189
Loss on disposal of assets										4,168	4,187
Other operating										347,820	267,191
Total operating expenses										2,258,875	1,878,295
Operating income										388,791	443,661
Other (income) expense:
Interest expense										57,302	41,654
Capitalized interest										(13,793)	(12,705)
Interest income										(8,736)	(5,276)
Other expense										366	528
Total other (income) expense										35,139	24,201
Income before income taxes										353,652	419,460
Provision (benefit) for income taxes										(66,954)	154,581
Net income										$ 420,606	$ 264,879
Basic earnings per share										$ 6.08	$ 3.77
Diluted earnings per share										$ 6.06	$ 3.76
Accounting Standards Update 2014-09 [Member] | Restatement Adjustment [Member]
Operating revenues:
Total operating revenues				$ (825)	$ (4)	$ (1,496)	$ (1,789)			$ (4,114)	$ (1,935)
Operating expenses:
Aircraft fuel				0	0	0	0			0	0
Salaries, wages and benefits				0	0	0	0			0	0
Aircraft rent				0	0	0	0			0	0
Landing fees and other rents				0	0	0	0			0	0
Depreciation and amortization				0	0	0	0			0	0
Maintenance, materials and repairs				0	0	0	0			0	0
Distribution				425	226	(73)	(726)			(148)	268
Special charges (credits)				0	0	0	0			0	0
Loss on disposal of assets				0	0	0	0			0	0
Other operating				0	0	0	0			0	0
Total operating expenses				425	226	(73)	(726)			(148)	268
Operating income				(1,250)	(230)	(1,423)	(1,063)			(3,966)	(2,203)
Other (income) expense:
Interest expense				0	0	0	0			0	0
Capitalized interest				0	0	0	0			0	0
Interest income				0	0	0	0			0	0
Other expense				0	0	0	0			0	0
Total other (income) expense				0	0	0	0			0	0
Income before income taxes				(1,250)	(230)	(1,423)	(1,063)			(3,966)	(2,203)
Provision (benefit) for income taxes				2,113	(84)	(522)	(389)			1,118	(807)
Net income				$ (3,363)	$ (146)	$ (901)	$ (674)			$ (5,084)	$ (1,396)
Basic earnings per share				$ (0.05)	$ 0	$ (0.01)	$ (0.01)			$ (0.07)	$ (0.02)
Diluted earnings per share				$ (0.05)	$ 0	$ (0.01)	$ (0.01)			$ (0.07)	$ (0.02)
Passenger [Member]
Operating revenues:
Total operating revenues	$ 887,956	836,350	689,141	$ 650,647	$ 669,072	$ 680,880	$ 572,287	$ 2,413,447	$ 1,922,239	$ 2,572,887	$ 2,257,801
Passenger [Member] | As Reported [Member]
Operating revenues:
Total operating revenues										1,366,034	1,200,621
Passenger [Member] | Accounting Standards Update 2014-09 [Member] | Restatement Adjustment [Member]
Operating revenues:
Total operating revenues				312,504	312,865	308,959	272,525			1,206,853	1,057,180
Other [Member]
Operating revenues:
Total operating revenues	$ 16,374	$ 15,421	$ 14,997	15,535	18,155	19,305	17,670	$ 46,792	$ 55,130	70,665	62,220
Other [Member] | As Reported [Member]
Operating revenues:
Total operating revenues										1,281,632	1,121,335
Other [Member] | Accounting Standards Update 2014-09 [Member] | Restatement Adjustment [Member]
Operating revenues:
Total operating revenues				$ (313,329)	$ (312,869)	$ (310,455)	$ (274,314)			$ (1,210,967)	$ (1,059,115)

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Revenue Recognition - Impact on Balance Sheets (Details) - USD ($) $ / shares in Units, $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 773,710	$ 800,849	$ 863,680	$ 700,900
Short-term investment securities	102,201	100,937		100,155
Accounts receivable, net	63,526	49,323		41,136
Aircraft maintenance deposits, net	104,472	175,615		87,035
Income tax receivable	78,506	69,844		0
Prepaid expenses and other current assets	83,692	85,542		48,321
Total current assets	1,206,107	1,282,110		977,547
Property and equipment:
Flight equipment	3,023,898	2,291,110		1,461,525
Ground property and equipment	178,339	155,166		126,206
Less accumulated depreciation	(296,157)	(207,808)		(122,509)
Total property and equipment	2,906,080	2,238,468		1,465,222
Deposits on flight equipment purchase contracts	253,825	253,687		325,688
Long-term aircraft maintenance deposits	144,642	150,617		199,415
Deferred heavy maintenance, net	191,632	99,915		75,534
Other long-term assets	79,445	121,003		110,223
Total assets	4,781,731	4,145,800		3,153,629
Current liabilities:
Accounts payable	63,190	22,822		15,193
Air traffic liability	323,627	263,711		220,184
Current maturities of long-term debt	150,200	115,430		84,354
Other current liabilities	287,142	262,370		226,011
Total current liabilities	824,821	664,333		545,742
Long-term debt and capital leases, less current maturities	1,770,500	1,387,498		897,359
Deferred income taxes	332,119	308,814		302,700
Deferred gains and other long-term liabilities	20,105	22,581		22,644
Shareholders’ equity:
Common stock	7	7		7
Additional paid-in-capital	368,451	360,153		551,004
Treasury stock, at cost	(66,999)	(65,854)		(218,692)
Retained earnings	1,533,545	1,469,732		1,054,210
Accumulated other comprehensive income (loss)	(1,222)	(1,464)		(1,345)
Total shareholders’ equity	1,833,782	1,762,574		1,385,184
Total liabilities and shareholders’ equity	$ 4,781,731	$ 4,145,800		$ 3,153,629
Common stock, par value (in dollars per share)		$ 0.0001		$ 0.0001
Common stock, shares authorized (in shares)		240,000,000		240,000,000
Common stock, shares issued (in shares)		69,770,795		73,549,872
Common stock, shares outstanding (in shares)		68,196,964		69,326,202
Treasury stock (in shares)		1,573,831		4,223,670
As Reported [Member]
Current assets:
Cash and cash equivalents		$ 800,849		$ 700,900
Short-term investment securities		100,937		100,155
Accounts receivable, net		49,323		41,136
Aircraft maintenance deposits, net		175,615		87,035
Income tax receivable		69,844		0
Prepaid expenses and other current assets		83,692		46,619
Total current assets		1,280,260		975,845
Property and equipment:
Flight equipment		2,291,110		1,461,525
Ground property and equipment		155,166		126,206
Less accumulated depreciation		(207,808)		(122,509)
Total property and equipment		2,238,468		1,465,222
Deposits on flight equipment purchase contracts		253,687		325,688
Long-term aircraft maintenance deposits		150,617		199,415
Deferred heavy maintenance, net		99,915		75,534
Other long-term assets		121,003		110,223
Total assets		4,143,950		3,151,927
Current liabilities:
Accounts payable		22,822		15,193
Air traffic liability		246,404		206,392
Current maturities of long-term debt		115,430		84,354
Other current liabilities		262,370		226,011
Total current liabilities		647,026		531,950
Long-term debt and capital leases, less current maturities		1,387,498		897,359
Deferred income taxes		313,140		308,143
Deferred gains and other long-term liabilities		19,205		19,868
Shareholders’ equity:
Common stock		7		7
Additional paid-in-capital		360,153		551,004
Treasury stock, at cost		(65,854)		(218,692)
Retained earnings		1,484,239		1,063,633
Accumulated other comprehensive income (loss)		(1,464)		(1,345)
Total shareholders’ equity		1,777,081		1,394,607
Total liabilities and shareholders’ equity		4,143,950		3,151,927
Accounting Standards Update 2014-09 [Member] | Restatement Adjustment [Member]
Current assets:
Cash and cash equivalents		0		0
Short-term investment securities		0		0
Accounts receivable, net		0		0
Aircraft maintenance deposits, net		0		0
Income tax receivable		0		0
Prepaid expenses and other current assets		1,850		1,702
Total current assets		1,850		1,702
Property and equipment:
Flight equipment		0		0
Ground property and equipment		0		0
Less accumulated depreciation		0		0
Total property and equipment		0		0
Deposits on flight equipment purchase contracts		0		0
Long-term aircraft maintenance deposits		0		0
Deferred heavy maintenance, net		0		0
Other long-term assets		0		0
Total assets		1,850		1,702
Current liabilities:
Accounts payable		0		0
Air traffic liability		17,307		13,792
Current maturities of long-term debt		0		0
Other current liabilities		0		0
Total current liabilities		17,307		13,792
Long-term debt and capital leases, less current maturities		0		0
Deferred income taxes		(4,326)		(5,443)
Deferred gains and other long-term liabilities		3,376		2,776
Shareholders’ equity:
Common stock		0		0
Additional paid-in-capital		0		0
Treasury stock, at cost		0		0
Retained earnings		(14,507)		(9,423)
Accumulated other comprehensive income (loss)		0		0
Total shareholders’ equity		(14,507)		(9,423)
Total liabilities and shareholders’ equity		$ 1,850		$ 1,702

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Revenue Recognition - Narrative (Details) $ in Thousands	3 Months Ended							9 Months Ended		12 Months Ended
	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Sep. 30, 2018 USD ($) revenue_arrangement	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jan. 01, 2018 USD ($)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Air traffic liability	$ 323,627			$ 263,711				$ 323,627		$ 263,711	$ 220,184
Credit shell term								60 days
Frequent Flyer Program, number of types of revenue arrangements | revenue_arrangement								2
Revenues	$ 904,330	$ 851,771	$ 704,138	$ 666,182	$ 687,227	$ 700,185	$ 589,957	$ 2,460,239	$ 1,977,369	$ 2,643,552	$ 2,320,021
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Air traffic liability												$ 12,400
Mileage Credit Programs [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues								$ 29,600	$ 38,100

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Revenue Disaggregation (Details) - USD ($) $ in Thousands	3 Months Ended							9 Months Ended		12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 904,330	$ 851,771	$ 704,138	$ 666,182	$ 687,227	$ 700,185	$ 589,957	$ 2,460,239	$ 1,977,369	$ 2,643,552	$ 2,320,021
DOT—Domestic [Member]
Disaggregation of Revenue [Line Items]
Total operating revenues	819,300				636,300			2,236,300	1,819,200
DOT—Latin America [Member]
Disaggregation of Revenue [Line Items]
Total operating revenues	85,000				50,900			223,900	158,200
As Reported [Member]
Disaggregation of Revenue [Line Items]
Total operating revenues										2,647,666	2,321,956
Accounting Standards Update 2014-09 [Member] | Restatement Adjustment [Member]
Disaggregation of Revenue [Line Items]
Total operating revenues				(825)	(4)	(1,496)	(1,789)			(4,114)	(1,935)
Passenger [Member]
Disaggregation of Revenue [Line Items]
Total operating revenues	887,956	836,350	689,141	650,647	669,072	680,880	572,287	2,413,447	1,922,239	2,572,887	2,257,801
Passenger [Member] | As Reported [Member]
Disaggregation of Revenue [Line Items]
Total operating revenues										1,366,034	1,200,621
Passenger [Member] | Accounting Standards Update 2014-09 [Member] | Restatement Adjustment [Member]
Disaggregation of Revenue [Line Items]
Total operating revenues				312,504	312,865	308,959	272,525			1,206,853	1,057,180
Fare [Member]
Disaggregation of Revenue [Line Items]
Total operating revenues	476,660	439,549	342,695	337,324	355,593	371,443	299,035			1,363,395	1,198,107
Fare [Member] | As Reported [Member]
Disaggregation of Revenue [Line Items]
Total operating revenues										1,366,034	1,200,621
Fare [Member] | Accounting Standards Update 2014-09 [Member] | Restatement Adjustment [Member]
Disaggregation of Revenue [Line Items]
Total operating revenues										(2,639)	(2,514)
Non Fare [Member]
Disaggregation of Revenue [Line Items]
Total operating revenues	411,296	396,801	346,446	313,323	313,479	309,437	273,252			1,209,492	1,059,694
Non Fare [Member] | As Reported [Member]
Disaggregation of Revenue [Line Items]
Total operating revenues										0	0
Non Fare [Member] | Accounting Standards Update 2014-09 [Member] | Restatement Adjustment [Member]
Disaggregation of Revenue [Line Items]
Total operating revenues										1,209,492	1,059,694
Other [Member]
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 16,374	$ 15,421	$ 14,997	15,535	18,155	19,305	17,670	$ 46,792	$ 55,130	70,665	62,220
Other [Member] | As Reported [Member]
Disaggregation of Revenue [Line Items]
Total operating revenues										1,281,632	1,121,335
Other [Member] | Accounting Standards Update 2014-09 [Member] | Restatement Adjustment [Member]
Disaggregation of Revenue [Line Items]
Total operating revenues				$ (313,329)	$ (312,869)	$ (310,455)	$ (274,314)			$ (1,210,967)	$ (1,059,115)

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Special Charges (Details) $ in Thousands	3 Months Ended						9 Months Ended		12 Months Ended
	Sep. 30, 2018 USD ($)	Mar. 31, 2018 USD ($) aircraft	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Sep. 30, 2018 USD ($) aircraft	Sep. 30, 2017 USD ($) aircraft	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Property, Plant and Equipment [Line Items]
Ratification Incentive							$ 80,200
Adjustments for contractual provisions							8,500
Special charges (credits)	$ (686)		$ 0	$ 7,853	$ 0	$ 4,776	88,656	$ 12,629	$ 12,629	$ 37,189
Ratification Incentive Paid							76,200
Purchase of property and equipment							420,586	428,913
Special charges, non-operating	$ 1,744			$ 0			$ 90,357	0
Airbus A319 [Member]
Property, Plant and Equipment [Line Items]
Purchase price		$ 285,000
Airbus A319 [Member] | Capital Lease Obligations [Member]
Property, Plant and Equipment [Line Items]
Number of aircrafts purchased | aircraft		14
Aircraft [Member]
Property, Plant and Equipment [Line Items]
Special charges (credits)								$ 7,900
Number of previously leased engines | aircraft							22	1
Purchase of property and equipment								$ 12,600
Value of noncash consideration								7,400
Fair value of assets acquired								11,900
Aircraft [Member] | Other Non-Cash Items [Member]
Property, Plant and Equipment [Line Items]
Value of noncash consideration								200
Aircraft [Member] | Airbus A319 [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment To Be Purchased, Consideration Transferred								20,000
Spare Engines [Member]
Property, Plant and Equipment [Line Items]
Number of previously leased engines | aircraft							1
Spare Engines [Member] | Spare Engines [Member]
Property, Plant and Equipment [Line Items]
Special charges (credits)								$ 4,800
Number of previously leased engines | aircraft								1
Purchase price								$ 8,100
Purchase of property and equipment								3,800
Value of noncash consideration								4,300
Fair value of assets acquired								3,100
Spare Engines [Member] | Spare Engines [Member] | Other Non-Cash Items [Member]
Property, Plant and Equipment [Line Items]
Value of noncash consideration								$ 200

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Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended					9 Months Ended		12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Numerator
Net income	$ 97,480	$ 246,975	$ 60,044	$ 77,241	$ 31,261	$ 63,812	$ 168,546	$ 415,522	$ 263,483
Denominator
Weighted-average shares outstanding, basic (in shares)	68,254		69,370			68,243	69,363
Effect of dilutive stock awards (in shares)	249		88			103	174
Adjusted weighted-average shares outstanding, diluted (in shares)	68,503		69,458			68,346	69,537
Net income per share
Basic earnings per common share (in dollars per share)	$ 1.43	$ 3.59	$ 0.87	$ 1.11	$ 0.45	$ 0.94	$ 2.43	$ 6.00	$ 3.75
Diluted earnings per common share (in dollars per share)	$ 1.42	$ 3.58	$ 0.86	$ 1.11	$ 0.45	$ 0.93	$ 2.42	$ 5.99	$ 3.74
Anti-dilutive weighted-average shares (in shares)	5		124			192	76

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Short-term Investment Securities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Debt Securities, Available-for-sale [Line Items]
Short-term investment securities	$ 102,201		$ 102,201		$ 100,937	$ 100,155
Unrealized gain (loss), net of deferred taxes	(7)	$ 13	70	$ (11)
Tax effect of the unrealized gain (loss) on short-term investment securities	(5)	$ 7	21	$ (6)
Accumulated other comprehensive loss	1,222		$ 1,222		1,464	$ 1,345
Available-for-sale Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Weighted-average fixed rate			1.50%
Accumulated other comprehensive loss	$ 34		$ 34		$ 105

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Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Salaries and wages	$ 81,278	$ 54,338
Federal excise and other passenger taxes and fees payable	55,743	42,036
Airport obligations	47,476	56,299
Aircraft maintenance	26,438	33,033
Fuel	21,637	25,171
Interest payable	18,965	11,384
Aircraft and facility lease obligations	12,236	16,992
Other	23,369	23,117
Other current liabilities	$ 287,142	$ 262,370	$ 226,011

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Financial Instruments and Risk Management - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Interest rate derivative losses reclassified into earnings	$ 52	$ 53	$ 172	$ 160
Loss reclassified from AOCI into earnings, tax	27	31	66	92
Accumulated other comprehensive loss	1,222		1,222		$ 1,464	$ 1,345
Interest Rate Swap [Member]
Derivative [Line Items]
Accumulated other comprehensive loss	1,200		1,200		$ 1,400
Interest Rate Swap [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Interest rate derivative losses reclassified into earnings	52	53	172	160
Loss reclassified from AOCI into earnings, tax	$ 27	$ 31	$ 66	$ 92

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Commitments and Contingencies - Schedule of Future Aircraft Operating Leases (Details)	Sep. 30, 2018 aircraft
Long-term Purchase Commitment [Line Items]
remainder of 2018	8
2019	15
2020	16
2021	18
Total future aircraft to be received	57
Airbus [Member] | A320 [Member]
Long-term Purchase Commitment [Line Items]
remainder of 2018	5
2019	2
2020
Total future aircraft to be received	7
Airbus [Member] | A320NEO [Member]
Long-term Purchase Commitment [Line Items]
2019	9
2020	16
2021	18
Total future aircraft to be received	43
Third Party Lessor [Member] | A320NEO [Member]
Long-term Purchase Commitment [Line Items]
remainder of 2018	3
2019	4
Total future aircraft to be received	7

XML

Commitments and Contingencies - Aircraft-Related Commitments and Financing Arrangements (Details)	1 Months Ended	3 Months Ended		9 Months Ended
	Jul. 31, 2015 aircraft seat	Jun. 30, 2018 USD ($) aircraft_engine	Mar. 31, 2018 USD ($) aircraft_engine aircraft	Sep. 30, 2018 USD ($) aircraft_engine aircraft	Sep. 30, 2017 USD ($) aircraft	Nov. 30, 2017 aircraft
Unrecorded Unconditional Purchase Obligation [Line Items]
Capital lease assets within flight equipment			$ 236,700,000
Capital lease obligation			$ 143,800,000
Number of engines ordered | aircraft_engine			6
Property, Plant And Equipment, Number Of Engines Purchased | aircraft_engine				6
Property, Plant And Equipment, Number Of Engines Sold | aircraft_engine		5
Principal and Interest Commitments
Number of Spare Engines Capitalized | aircraft				6
Estimated Remaining Project Construction Costs				$ 0
Spare Engines [Member]
Principal and Interest Commitments
Number of leased assets | aircraft_engine				12
Secured Debt [Member]
Interest Commitments
Interest commitments, 2018				$ 21,600,000
Interest commitments, 2019				76,300,000
Interest commitments, 2020				69,700,000
Interest commitments, 2021				63,200,000
Interest commitments, 2022				56,800,000
Interest commitments, 2023 and beyond				179,400,000
Principal and Interest Commitments
Principal and interest commitments related to future secured debt, 2018				0
Principal and interest commitments related to future secured debt, 2019				4,400,000
Principal and interest commitments related to future secured debt, 2020				4,000,000.0
Principal and interest commitments related to future secured debt, 2021				3,300,000
Principal and interest commitments related to future secured debt, 2022				3,100,000
Principal and interest commitments related to future secured debt, 2023 and beyond				$ 34,000,000.0
Aircraft [Member]
Principal and Interest Commitments
Number of Aircraft Capitalized | aircraft				77
Number of Previously Leased Aircraft or Engine Purchased | aircraft				22	1
Operating Leases of Lessee, Number of Assets Leased, Affected by Variable Rate Basis | aircraft				1
2018 [Member] | Airbus [Member]
Aircraft rent commitments
Number of aircraft with secured debt financing commitments scheduled for delivery | aircraft				1
2019-2021 [Member] [Member] | Airbus [Member]
Aircraft rent commitments
Number of aircraft without secured financing commitments scheduled for delivery | aircraft				49
Aircraft and Related Flight Equipment [Member]
Committed Expenditures
Committed expenditures, remainder of 2018				$ 210,200,000
Committed expenditures, 2019				592,100,000
Committed expenditures, 2020				810,800,000
Committed expenditures, 2021				775,400,000
Committed expenditures, 2022				17,000,000.0
Committed expenditures, 2023 and beyond				8,000,000.0
Aircraft and Related Flight Equipment [Member] | Enhanced Equipment Trust Certificate [Member]
Committed Expenditures
Face amount, commitment for future issuance				39,100,000
Fixed Maintenance Reserve Payments, Aircraft and Related Flight Equipment [Member]
Committed Expenditures
Committed expenditures, remainder of 2018				1,800,000
Committed expenditures, 2019				5,800,000
Committed expenditures, 2020				5,600,000
Committed expenditures, 2021				5,700,000
Committed expenditures, 2022				4,900,000
Committed expenditures, 2023 and beyond				12,900,000
Non-aircraft Related Commitments [Member]
Committed Expenditures
Committed expenditures, remainder of 2018				2,500,000
Committed expenditures, 2019				12,600,000
Committed expenditures, 2020				12,700,000
Committed expenditures, 2021				9,900,000
Committed expenditures, 2022				10,000,000.0
Committed expenditures, 2023 and beyond				$ 66,600,000
V2500 SelectOne Engine [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Proceeds from Sale of Other Property, Plant, and Equipment		$ 9,500,000
Loss on sale of engines		$ 4,400,000
V2500 SelectTWO Engine [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of spare aircraft engines ordered | aircraft_engine				2
PurePower PW1100G-JM Engine [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of spare aircraft engines ordered | aircraft_engine				9
Spare Engines [Member]
Principal and Interest Commitments
Number of Previously Leased Aircraft or Engine Purchased | aircraft				1
Spare Engines [Member] | Spare Engines [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Purchase price					$ 8,100,000
Principal and Interest Commitments
Number of Previously Leased Aircraft or Engine Purchased | aircraft					1
A-320-Neo [Member] | Third Party Lessor [Member]
Aircraft rent commitments
Aircraft rent commitments, remainder of 2018				$ 1,000,000.0
Aircraft rent commitments, 2019				27,200,000
Aircraft rent commitments, 2020				29,400,000
Aircraft rent commitments, 2021				29,400,000
Aircraft rent commitments, 2022				29,400,000
Aircraft rent commitments, 2023 and beyond				$ 235,900,000
A-320-Neo [Member] | 2019 [Member] | Airbus [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Aircraft scheduled for delivery | aircraft				14
Airbus A319 [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Purchase price			$ 285,000,000.0
Airbus A319 [Member] | Capital Lease Obligations [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of aircrafts purchased | aircraft			14
A320 and A321 [Member] | Airbus [Member]
Aircraft rent commitments
Number of delivered aircraft with secured debt financing commitments | aircraft				55
A320 [Member] | Airbus [Member]
Principal and Interest Commitments
Number of aircrafts with increased seating capacity | aircraft	40
A320 [Member] | Airbus [Member] | Minimum [Member]
Principal and Interest Commitments
Number of seats | seat	178
A320 [Member] | Airbus [Member] | Maximum [Member]
Principal and Interest Commitments
Number of seats | seat	182
A320 [Member] | 2018 [Member] | Equipment Notes, 2017-1 [Member]
Aircraft rent commitments
Number of aircraft with secured debt financing commitments scheduled for delivery | aircraft				1		1
A320 Family [Member]
Principal and Interest Commitments
Number of Aircraft Held | aircraft				121
A320 Family [Member] | Aircraft [Member]
Principal and Interest Commitments
Number of leased assets | aircraft				44
Aircraft order contract renegotiation [Member] | Airbus A320 [Member] | Airbus [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of Aircraft Order Conversions | aircraft				5

XML

Commitments and Contingencies - Future Minimum Lease Payments Under Capital Leases and Noncancelable Operating Leases (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($)
Operating Leased Assets [Line Items]
Lease term	3 years
Total Operating and Capital Lease Obligations
remainder of 2018	$ 58,049
2019	213,003
2020	191,761
2021	176,858
2022	161,307
2023 and thereafter	521,822
Total minimum lease payments	1,322,800
Fixed Maintenance Reserve Payments, Aircraft and Related Flight Equipment [Member]
Committed Expenditures
Committed expenditures, remainder of 2018	1,800
Committed expenditures, 2019	5,800
Committed expenditures, 2020	5,600
Committed expenditures, 2021	5,700
Committed expenditures, 2022	4,900
Committed expenditures, 2023 and beyond	12,900
Non-aircraft Related Commitments [Member]
Committed Expenditures
Committed expenditures, remainder of 2018	2,500
Committed expenditures, 2019	12,600
Committed expenditures, 2020	12,700
Committed expenditures, 2021	9,900
Committed expenditures, 2022	10,000
Committed expenditures, 2023 and beyond	66,600
Capital Lease Obligations [Member]
Capital Leases
remainder of 2018	165
2019	625
2020	249
2021	28
2022	0
2023 and thereafter	0
Total minimum lease payments	1,067
Less amount representing interest	49
Present value of minimum lease payments	1,018
Less current portion	596
Long-term portion	422
Aircraft and Spare Engine Leases [Member]
Operating Leases
remainder of 2018	42,762
2019	167,360
2020	161,876
2021	160,185
2022	146,904
2023 and thereafter	419,925
Total minimum lease payments	1,099,012
Property Facility Leases [Member]
Operating Leases
remainder of 2018	15,122
2019	45,018
2020	29,636
2021	16,645
2022	14,403
2023 and thereafter	101,897
Total minimum lease payments	$ 222,721

XML

Commitments and Contingencies - Credit Card Processing Arrangements (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Restricted cash holdbacks	$ 0	$ 0
Maximum Potential Exposure to Cash Holdbacks from Credit Card Processors	$ 341,500,000	$ 286,300,000

XML

Commitments and Contingencies - Employees (Details) $ in Millions	1 Months Ended		9 Months Ended
	Oct. 31, 2018	Feb. 28, 2018	Sep. 30, 2018 USD ($) employee_group	Dec. 31, 2017 USD ($)
Air Line Pilots Association, International [Member]
Concentration Risk [Line Items]
Term of collective bargaining agreement		5 years
Professional Airline Flight Control Association [Member] | Subsequent Event [Member]
Concentration Risk [Line Items]
Term of collective bargaining agreement	5 years
Health Insurance
Liability for Claims and Claims Adjustment Expense [Line Items]
Accrued health care claims | $			$ 5.6	$ 3.9
Unionized Employees Concentration Risk [Member] | Number of Employees, Total [Member]
Concentration Risk [Line Items]
Number of union-represented employee groups | employee_group			4
Company's employees covered under collective bargaining agreements (as a percent)			76.00%
Unionized Employees Concentration Risk [Member] | Number of Employees, Total [Member] | Air Line Pilots Association, International [Member]
Concentration Risk [Line Items]
Company's employees covered under collective bargaining agreements (as a percent)			27.00%
Unionized Employees Concentration Risk [Member] | Number of Employees, Total [Member] | Association of Flight Attendants [Member]
Concentration Risk [Line Items]
Company's employees covered under collective bargaining agreements (as a percent)			44.00%
Unionized Employees Concentration Risk [Member] | Number of Employees, Total [Member] | Professional Airline Flight Control Association [Member]
Concentration Risk [Line Items]
Company's employees covered under collective bargaining agreements (as a percent)			1.00%
Unionized Employees Concentration Risk [Member] | Number of Employees, Total [Member] | International Association Of Machinists And Aerospace Workers (IAM) [Member]
Concentration Risk [Line Items]
Company's employees covered under collective bargaining agreements (as a percent)			4.00%

XML

Fair Value Measurements - Long-term Debt (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Carrying Value	$ 1,964.6	$ 1,539.6
Senior Loans [Member]
Debt Instrument [Line Items]
Carrying Value	391.4	417.9
Junior Loans [Member]
Debt Instrument [Line Items]
Carrying Value	33.2	39.3
Fixed Rate Loan [Member]
Debt Instrument [Line Items]
Carrying Value	493.9	518.0
Equipment Notes, Series A 2015-1 [Member]
Debt Instrument [Line Items]
Carrying Value	393.6	408.6
Equipment Notes, Series B 2015-1 [Member]
Debt Instrument [Line Items]
Carrying Value	84.0	92.0
Equipment Notes, Series C 2015-1 [Member]
Debt Instrument [Line Items]
Carrying Value	115.2	0.0
Equipment Notes, Series AA 2017-1 [Member]
Debt Instrument [Line Items]
Carrying Value	223.3	37.5
Equipment Notes, Series A 2017-1 [Member]
Debt Instrument [Line Items]
Carrying Value	74.4	12.5
Equipment Notes, Series B 2017-1 [Member]
Debt Instrument [Line Items]
Carrying Value	76.7	13.8
Equipment Notes, Series C 2017-1 [Member]
Debt Instrument [Line Items]
Carrying Value	78.9	0.0
Estimated Fair Value [Member]
Debt Instrument [Line Items]
Estimated Fair Value	1,940.3	1,583.2
Estimated Fair Value [Member] | Level 3 [Member] | Senior Loans [Member]
Debt Instrument [Line Items]
Estimated Fair Value	395.5	435.3
Estimated Fair Value [Member] | Level 3 [Member] | Junior Loans [Member]
Debt Instrument [Line Items]
Estimated Fair Value	33.6	40.4
Estimated Fair Value [Member] | Level 3 [Member] | Fixed Rate Loan [Member]
Debt Instrument [Line Items]
Estimated Fair Value	487.2	528.6
Estimated Fair Value [Member] | Level 2 [Member] | Equipment Notes, Series A 2015-1 [Member]
Debt Instrument [Line Items]
Estimated Fair Value	389.8	420.9
Estimated Fair Value [Member] | Level 2 [Member] | Equipment Notes, Series B 2015-1 [Member]
Debt Instrument [Line Items]
Estimated Fair Value	83.5	94.2
Estimated Fair Value [Member] | Level 2 [Member] | Equipment Notes, Series C 2015-1 [Member]
Debt Instrument [Line Items]
Estimated Fair Value	114.4	0.0
Estimated Fair Value [Member] | Level 2 [Member] | Equipment Notes, Series AA 2017-1 [Member]
Debt Instrument [Line Items]
Estimated Fair Value	213.6	37.4
Estimated Fair Value [Member] | Level 2 [Member] | Equipment Notes, Series A 2017-1 [Member]
Debt Instrument [Line Items]
Estimated Fair Value	71.1	12.6
Estimated Fair Value [Member] | Level 2 [Member] | Equipment Notes, Series B 2017-1 [Member]
Debt Instrument [Line Items]
Estimated Fair Value	73.3	13.8
Estimated Fair Value [Member] | Level 2 [Member] | Equipment Notes, Series C 2017-1 [Member]
Debt Instrument [Line Items]
Estimated Fair Value	$ 78.3	$ 0.0

XML

Fair Value Measurements - Assets and Liabilities Measured on Recurring Basis (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 773.7	$ 800.8
Short-term investment securities	102.2	100.9
Total assets	875.9	901.7
Total liabilities	0.0	0.0
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	773.7	800.8
Short-term investment securities	102.2	100.9
Total assets	875.9	901.7
Total liabilities	0.0	0.0
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0.0	0.0
Short-term investment securities	0.0	0.0
Total assets	0.0	0.0
Total liabilities	0.0	0.0
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0.0	0.0
Short-term investment securities	0.0	0.0
Total assets	0.0	0.0
Total liabilities	$ 0.0	$ 0.0

XML

Debt and Other Obligations (Details) $ in Thousands	1 Months Ended		3 Months Ended		9 Months Ended
	May 31, 2018 USD ($) aircraft agreement	Nov. 30, 2017 USD ($) aircraft trust	Sep. 30, 2018 USD ($) aircraft	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) aircraft	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Long-term debt			$ 1,964,600		$ 1,964,600		$ 1,539,600
Less current maturities			150,200		150,200		115,430	$ 84,354
Less unamortized discounts			43,900		43,900		36,700
Total			1,770,500		1,770,500		1,387,498	$ 897,359
Repayments of debt obligations			32,600	$ 13,400	93,200	$ 63,400
Equipment Notes, 2017-1 Series AA, A and B [Member] | Enhanced Equipment Trust Certificate [Member]
Debt Instrument [Line Items]
Number of pass-through trusts | trust		3
Debt financing commitments		$ 420,500
Principal amount			388,000		388,000
Senior Loans [Member]
Debt Instrument [Line Items]
Long-term debt			$ 391,400		$ 391,400		417,900
Weighted-average interest rate			4.10%	4.10%	4.10%	4.10%
Junior Loans [Member]
Debt Instrument [Line Items]
Long-term debt			$ 33,200		$ 33,200		39,300
Weighted-average interest rate			6.90%	6.90%	6.90%	6.90%
Fixed Rate Loan [Member]
Debt Instrument [Line Items]
Long-term debt			$ 493,900		$ 493,900		518,000
Weighted-average interest rate			3.83%	3.76%	3.83%	3.76%
Equipment Notes, Series A 2015-1 [Member]
Debt Instrument [Line Items]
Long-term debt			$ 393,600		$ 393,600		408,600
Weighted-average interest rate			4.10%	4.10%	4.10%	4.10%
Equipment Notes, Series B 2015-1 [Member]
Debt Instrument [Line Items]
Long-term debt			$ 84,000		$ 84,000		92,000
Weighted-average interest rate			4.45%	4.45%	4.45%	4.45%
Equipment Notes, Series C 2015-1 [Member]
Debt Instrument [Line Items]
Number of separation participation agreement amendments | agreement	15
Long-term debt			$ 115,200		$ 115,200		0
Weighted-average interest rate			4.93%		4.93%
Equipment Notes, Series C 2015-1 [Member] | Enhanced Equipment Trust Certificate [Member]
Debt Instrument [Line Items]
Stated interest rate			4.93%		4.93%
Principal amount	$ 115,200
Equipment Notes, Series AA 2017-1 [Member]
Debt Instrument [Line Items]
Long-term debt			$ 223,300		$ 223,300		37,500
Weighted-average interest rate			3.38%		3.38%
Equipment Notes, Series AA 2017-1 [Member] | Enhanced Equipment Trust Certificate [Member]
Debt Instrument [Line Items]
Stated interest rate			3.375%		3.375%
Equipment Notes, Series A 2017-1 [Member]
Debt Instrument [Line Items]
Long-term debt			$ 74,400		$ 74,400		12,500
Weighted-average interest rate			3.65%		3.65%
Equipment Notes, Series A 2017-1 [Member] | Enhanced Equipment Trust Certificate [Member]
Debt Instrument [Line Items]
Stated interest rate			3.65%		3.65%
Equipment Notes, Series B 2017-1 [Member]
Debt Instrument [Line Items]
Long-term debt			$ 76,700		$ 76,700		13,800
Weighted-average interest rate			3.80%		3.80%
Equipment Notes, Series B 2017-1 [Member] | Enhanced Equipment Trust Certificate [Member]
Debt Instrument [Line Items]
Stated interest rate			3.80%		3.80%
Equipment Notes, Series C 2017-1 [Member]
Debt Instrument [Line Items]
Number of separation participation agreement amendments | agreement	9
Long-term debt			$ 78,900		$ 78,900		$ 0
Weighted-average interest rate			5.11%		5.11%
Equipment Notes, Series C 2017-1 [Member] | Enhanced Equipment Trust Certificate [Member]
Debt Instrument [Line Items]
Stated interest rate			5.11%		5.11%
Debt commitment principal amount	$ 85,500
Principal amount	$ 65,700		$ 13,200		$ 13,200
A320 [Member] | Equipment Notes, 2017-1 [Member] | Enhanced Equipment Trust Certificate [Member]
Debt Instrument [Line Items]
Number of aircraft with secured debt financing commitments scheduled for delivery | aircraft		7
Number of delivered aircraft with secured debt financing commitments | aircraft			6		6
A321 [Member] | Equipment Notes, 2017-1 [Member] | Enhanced Equipment Trust Certificate [Member]
Debt Instrument [Line Items]
Number of aircraft with secured debt financing commitments scheduled for delivery | aircraft		5
Number of delivered aircraft with secured debt financing commitments | aircraft			5		5
Capital Addition Purchase Commitments [Member] | Enhanced Equipment Trust Certificate [Member]
Debt Instrument [Line Items]
Debt financing commitments			$ 39,100		$ 39,100
Capital Addition Purchase Commitments [Member] | Equipment Notes, 2017-1 Series AA, A and B [Member] | Enhanced Equipment Trust Certificate [Member]
Debt Instrument [Line Items]
Debt financing commitments			32,500		32,500
Capital Addition Purchase Commitments [Member] | Equipment Notes, Series C 2017-1 [Member] | Enhanced Equipment Trust Certificate [Member]
Debt Instrument [Line Items]
Debt financing commitments			$ 6,600		$ 6,600
February 2018 To March 2018 [Member] | A321 [Member] | Equipment Notes, 2017-1 [Member]
Debt Instrument [Line Items]
Number of aircraft with secured debt financing commitments scheduled for delivery | aircraft		5
February 2018 To March 2018 [Member] | A321 [Member] | Equipment Notes, 2017-1 [Member] | Enhanced Equipment Trust Certificate [Member]
Debt Instrument [Line Items]
Number of delivered aircraft with secured debt financing commitments | aircraft	5
December 2017 To January 2018 [Member] | A320 [Member] | Equipment Notes, 2017-1 [Member]
Debt Instrument [Line Items]
Number of aircraft with secured debt financing commitments scheduled for delivery | aircraft		3
April 2018 to August 2018 [Member] | A320 [Member] | Equipment Notes, 2017-1 [Member]
Debt Instrument [Line Items]
Number of aircraft with secured debt financing commitments scheduled for delivery | aircraft		3
October 2015 to January 2017 [Member] | A321 [Member] | Equipment notes, 2015-1 [Member] | Enhanced Equipment Trust Certificate [Member]
Debt Instrument [Line Items]
Number of delivered aircraft with secured debt financing commitments | aircraft	12
2018 [Member] | A320 [Member] | Equipment Notes, 2017-1 [Member]
Debt Instrument [Line Items]
Number of aircraft with secured debt financing commitments scheduled for delivery | aircraft		1	1		1
March 2016 to June 2016 [Member] | A320 [Member] | Equipment notes, 2015-1 [Member] | Enhanced Equipment Trust Certificate [Member]
Debt Instrument [Line Items]
Number of delivered aircraft with secured debt financing commitments | aircraft	3
December 2017 to April 2018 [Member] | A320 [Member] | Equipment Notes, 2017-1 [Member] | Enhanced Equipment Trust Certificate [Member]
Debt Instrument [Line Items]
Number of delivered aircraft with secured debt financing commitments | aircraft	4
October 2018 [Member] | A320 [Member] | Equipment Notes, 2017-1 [Member] | Enhanced Equipment Trust Certificate [Member]
Debt Instrument [Line Items]
Number of delivered aircraft with secured debt financing commitments | aircraft			2		2

XML

Debt and Other Obligations - Future Maturities (Details) $ in Millions	Sep. 30, 2018 USD ($)
Debt Disclosure [Abstract]
remainder of 2018	$ 44.0
2019	158.3
2020	155.3
2021	151.0
2022	147.9
2023 and beyond	1,308.1
Total debt principal payments	$ 1,964.6

XML

Debt and Other Obligations - Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Debt Instrument [Line Items]
Commitment fees	$ 50	$ 29	$ 153	$ 87
Amortization of debt discounts	1,784	1,362	4,930	3,883
Total	21,910	14,996	60,189	41,107
Senior Loans [Member]
Debt Instrument [Line Items]
Interest expense, term loans	4,195	4,564	12,769	13,854
Junior Loans [Member]
Debt Instrument [Line Items]
Interest expense, term loans	605	746	1,908	2,323
Fixed Rate Loan [Member]
Debt Instrument [Line Items]
Interest expense, term loans	4,844	2,811	14,636	4,555
Equipment Notes, Series A 2015-1 [Member]
Debt Instrument [Line Items]
Interest expense, term loans	4,057	4,366	12,214	12,995
Equipment Notes, Series B 2015-1 [Member]
Debt Instrument [Line Items]
Interest expense, term loans	939	1,118	2,881	3,410
Equipment Notes, Series C 2015-1 [Member]
Debt Instrument [Line Items]
Interest expense, term loans	1,420	0	2,209	0
Equipment Notes, Series AA 2017-1 [Member]
Debt Instrument [Line Items]
Interest expense, term loans	1,751	0	4,008	0
Equipment Notes, Series A 2017-1 [Member]
Debt Instrument [Line Items]
Interest expense, term loans	631	0	1,445	0
Equipment Notes, Series B 2017-1 [Member]
Debt Instrument [Line Items]
Interest expense, term loans	700	0	1,636	0
Equipment Notes, Series C 2017-1 [Member]
Debt Instrument [Line Items]
Interest expense, term loans	$ 934	$ 0	$ 1,400	$ 0

XML

Subsequent Event (Details) - Subsequent Event [Member]	Oct. 24, 2018 USD ($)	Oct. 23, 2018 USD ($) aircraft
Subsequent Event [Line Items]
Number of aircraft related to PDPs | aircraft		43
Revolving Credit Facility [Member]
Subsequent Event [Line Items]
Borrowing capacity (up to)		$ 160,000,000
Amounts drawn	$ 0