Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating activities:
Net loss	$ (146,004)	$ (162,031)	$ (171,995)
Adjustments to reconcile net loss to cash provided by (used in) operating activities:
Depreciation and amortization	118,817	133,617	145,490
Loss on asset disposals, abandonments and write-downs	13,851	13,352	8,960
Gain on transition to airline-directed model		(21,551)
Deferred income taxes	178	(3,821)	(2,281)
Stock-based compensation expense	16,511	16,912	19,821
Amortization of deferred financing costs	5,260	4,280	3,743
Accretion and amortization of debt discount and premium	14,711	18,255	18,286
Loss on extinguishment of debt	57,962	19,653
Changes in operating assets and liabilities:
Accounts receivable	29,898	(17,064)	(43,798)
Inventories	29,092	(50,762)	4,723
Prepaid expenses and other current assets	(630)	(3,106)	4,990
Contract assets	(21,863)	(30,485)
Accounts payable	(4,111)	(3,864)	3,402
Accrued liabilities	(11,452)	13,281	24,941
Deferred airborne lease incentives	(3,645)	(7,705)	20,407
Deferred revenue	(4,971)	(1,021)	21,477
Accrued interest	(29,646)	(955)	7,213
Warranty reserves	3,875	8,009	(152)
Other non-current assets and liabilities	(3,772)	(7,305)	(4,971)
Net cash provided by (used in) operating activities	64,061	(82,311)	60,256
Investing activities:
Purchases of property and equipment	(100,123)	(108,632)	(252,375)
Acquisition of intangible assets—capitalized software	(15,355)	(23,031)	(27,855)
Purchases of short-term investments		(39,323)	(317,418)
Redemptions of short-term investments	39,323	212,792	443,103
Other, net	2,446		(2,850)
Net cash provided by (used in) investing activities	(73,709)	41,806	(157,395)
Financing activities:
Proceeds from issuance of senior secured notes	920,683		181,754
Redemption of senior secured notes	(741,360)
Proceeds from issuance of convertible notes		237,750
Redemption of convertible notes	(159,502)	(200,438)
Payment of debt issuance costs	(22,976)	(8,054)	(3,630)
Payments on financing leases	(713)	(2,340)	(2,961)
Stock-based compensation activity	325	396	(227)
Net cash provided by (used in) financing activities	(3,543)	27,314	174,936
Effect of exchange rate changes on cash	(250)	578	743
Increase (decrease) in cash, cash equivalents and restricted cash	(13,441)	(12,613)	78,540
Cash, cash equivalents and restricted cash at beginning of period	191,116	203,729	125,189
Cash, cash equivalents and restricted cash at end of period	177,675	191,116	203,729
Cash, cash equivalents and restricted cash at end of period	191,116	203,729	125,189
Less: current restricted cash	560	1,535	500
Less: non-current restricted cash	7,099	5,426	6,873
Cash and cash equivalents at end of period	170,016	184,155	196,356
Supplemental Cash Flow Information:
Cash paid for interest	140,833	101,489	86,359
Cash paid for taxes	490	401	103
Non-cash Investing and Financing Activities:
Purchases of property and equipment in current liabilities	11,176	18,640	53,682
Purchases of property and equipment paid by commercial airlines	$ 19,287	$ 7,474	$ 23,762