Condensed Consolidating Financial Information - Guarantor Subsidiaries - Condensed Consolidating Statements of Cash Flows (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by operating activities	$ 119,519		$ 105,096		$ 50,550
Investing activities:
Purchase of property and equipment	(157,690)		(102,726)		(128,475)
Proceeds from asset dispositions	10,266		42,197		11,302
Purchase of short-term investments	(465,094)		(375,503)		(216,265)
Proceeds from sale of short-term investments	363,110		338,970		249,041
Refund of deposits on aircraft	11,506		8,161		2,500
Payments of deposits on aircraft	(6,948)		(9,318)		(8,717)
Loan to unconsolidated affiliate	(200)				(975)
Other	(200)				(50)
Net cash used in investing activities	(245,050)		(98,219)		(91,639)
Financing activities:
Proceeds from issuance of Senior Notes due 2019	500,000
Repayment of Senior Notes due 2018	(300,000)
Premium and cost to retire debt early	(26,749)
Debt issuance costs	(6,232)
Proceeds from line of credit	264,253		164,771		127,323
Payments on line of credit	(300,253)		(172,526)		(86,615)
Repurchase of common stock	(152)		(1,037)		(1,861)
Net cash provided by (used in) financing activities	130,867		(8,792)		38,847
(Decrease) increase in cash	5,336		(1,915)		(2,242)
Cash, beginning of year	934		2,849		5,091
Cash, end of year	6,270		934		2,849
Parent Company Only (issuer) [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by operating activities	51,476		82,660		15,781
Investing activities:
Purchase of property and equipment	(157,690)		(102,726)		(128,475)
Proceeds from asset dispositions	10,266		42,197		11,302
Purchase of short-term investments	(465,094)		(375,503)		(216,265)
Proceeds from sale of short-term investments	363,110		338,970		249,041
Refund of deposits on aircraft	11,506		8,161		2,500
Payments of deposits on aircraft	(6,948)		(9,318)		(8,717)
Loan to unconsolidated affiliate					(975)
Other	(200)				(50)
Net cash used in investing activities	(245,050)		(98,219)		(91,639)
Financing activities:
Proceeds from issuance of Senior Notes due 2019	500,000
Repayment of Senior Notes due 2018	(300,000)
Premium and cost to retire debt early	(26,749)
Debt issuance costs	(6,232)
Proceeds from line of credit	264,253		164,771		127,323
Payments on line of credit	(300,253)		(172,526)		(86,615)
Repurchase of common stock	(152)		(1,037)		(1,861)
Due to/from affiliate, net	(62,706)		23,851		33,250
Net cash provided by (used in) financing activities	193,573		15,059		72,097
(Decrease) increase in cash	(1)		(500)		(3,761)
Cash, beginning of year	52		552		4,313
Cash, end of year	51		52		552
Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by operating activities	68,043	[1],[2]	22,436	[1],[2]	34,769	[1],[2]
Financing activities:
Due to/from affiliate, net	62,706	[1],[2]	(23,851)	[1],[2]	(33,250)	[1],[2]
Net cash provided by (used in) financing activities	(62,706)	[1],[2]	(23,851)	[1],[2]	(33,250)	[1],[2]
(Decrease) increase in cash	5,337	[1],[2]	(1,415)	[1],[2]	1,519	[1],[2]
Cash, beginning of year	882	[1],[2]	2,297	[1],[2]	778	[1],[2]
Cash, end of year	$ 6,219	[1],[2]	$ 882	[1],[2]	$ 2,297	[1],[2]

[1] Foreign subsidiaries represent minor subsidiaries and are included in the guarantors' subsidiaries amounts.

[2] Cash flows between the Parent Company and Guarantor Subsidiaries related to the Company's centralized cash management activities in 2013 and 2012 have been adjusted to show the effects on net cash provided by operating and financing activities.