Condensed Consolidating Financial Information - Guarantor Subsidiaries - Condensed Consolidating Statements of Cash Flows (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Cash Flow Statements, Captions [Line Items]
Net cash (used in) provided by operating activities		$ (564)	$ 133,918	$ 119,519
Investing activities:
Purchase of property and equipment		(81,842)	(57,123)	(157,690)
Proceeds from asset dispositions		14,983	5,236	10,266
Purchase of short-term investments		(321,453)	(608,649)	(465,094)
Proceeds from sale of short-term investments		316,543	505,966	363,110
Refund of deposits on aircraft			6,010	11,506
Payments of deposits on aircraft		(2,249)	(1,273)	(6,948)
Loan to unconsolidated affiliate		(1,200)		(200)
Net cash used in investing activities		(75,218)	(149,833)	(245,050)
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		264,700	232,660	264,253
Payments on line of credit		(188,200)	(218,160)	(300,253)
Repurchase of common stock		(529)	(2,448)	(152)
Net cash provided by (used in) financing activities		75,971	12,052	130,867
(Decrease) increase in cash		189	(3,863)	5,336
Cash, beginning of year		2,407	6,270	934
Cash, end of year		2,596	2,407	6,270
Parent Company Only (issuer) [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash (used in) provided by operating activities		(46,738)	60,241	51,476
Investing activities:
Purchase of property and equipment		(81,484)	(57,123)	(157,690)
Proceeds from asset dispositions		14,983	5,236	10,266
Purchase of short-term investments		(321,453)	(608,649)	(465,094)
Proceeds from sale of short-term investments		316,543	505,966	363,110
Refund of deposits on aircraft			6,010	11,506
Payments of deposits on aircraft		(2,249)	(1,273)	(6,948)
Loan to unconsolidated affiliate		(1,200)		(200)
Net cash used in investing activities		(74,860)	(149,833)	(245,050)
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		264,700	232,660	264,253
Payments on line of credit		(188,200)	(218,160)	(300,253)
Repurchase of common stock		(529)	(2,448)	(152)
Due to/from affiliate, net		45,617	77,535	62,706
Net cash provided by (used in) financing activities		121,588	89,587	193,573
(Decrease) increase in cash		(10)	(5)	(1)
Cash, beginning of year		46	51	52
Cash, end of year		36	46	51
Guarantor Subsidiaries [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash (used in) provided by operating activities	[1]	46,174	73,677	68,043
Investing activities:
Purchase of property and equipment	[1]	(358)
Net cash used in investing activities	[1]	(358)
Financing activities:
Due to/from affiliate, net	[1]	(45,617)	(77,535)	(62,706)
Net cash provided by (used in) financing activities	[1]	(45,617)	(77,535)	(62,706)
(Decrease) increase in cash	[1]	199	(3,858)	5,337
Cash, beginning of year	[1]	2,361	6,219	882
Cash, end of year	[1]	$ 2,560	$ 2,361	$ 6,219

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