Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating activities:
Net income	$ 264,879	$ 317,220	$ 225,464
Adjustments to reconcile net income to net cash provided by operations:
Unrealized losses on open derivative contracts, net	0	2,202	0
Losses reclassified from other comprehensive income	354	132	0
Equity-based compensation	7,105	9,222	8,797
Allowance for doubtful accounts (recoveries)	80	12	(45)
Amortization of deferred gains and losses and debt issuance costs	5,732	1,165	(185)
Depreciation and amortization	101,136	73,908	46,971
Deferred income tax expense	86,146	155,614	34,118
Loss on disposal of assets	4,187	1,604	3,008
Lease termination costs	37,189	0	0
Changes in operating assets and liabilities:
Accounts receivable	(12,951)	(5,592)	606
Aircraft maintenance deposits	(45,869)	(32,101)	(31,925)
Long-term deposits and other assets	(75,780)	(103,613)	(48,382)
Prepaid income taxes	72,278	0	0
Accounts payable	(6,823)	2,706	(10,034)
Air traffic liability	(11,582)	36,387	21,135
Other liabilities	47,391	14,119	12,302
Other	206	0	0
Net cash provided by operating activities	473,678	472,985	261,830
Investing activities:
Purchase of short-term investment securities	(103,258)	0	0
Proceeds from the maturity of short-term investment securities	2,842	0	0
Proceeds from sale of property and equipment	50	0	0
Pre-delivery deposits for flight equipment, net of refunds	(173,947)	(142,323)	(115,802)
Capitalized interest	(10,834)	(10,159)	(1,318)
Purchase of property and equipment	(541,122)	(548,800)	(186,569)
Net cash used in investing activities	(826,269)	(701,282)	(303,689)
Financing activities:
Proceeds from issuance of long-term debt	417,275	536,780	148,000
Proceeds from stock options exercised	92	32	174
Payments on debt and capital lease obligations	(64,421)	(26,364)	(1,233)
Proceeds from sale leaseback transactions	0	7,300	7,200
Payments to pre-IPO shareholders pursuant to tax receivable agreement	0	0	(5,643)
Excess tax (deficiency) benefit from equity-based compensation	(470)	8,850	1,871
Repurchase of common stock	(102,510)	(112,261)	(1,630)
Debt issuance costs	(107)	(15,192)	(4,727)
Net cash provided by financing activities	249,859	399,145	144,012
Net (decrease) increase in cash and cash equivalents	(102,732)	170,848	102,153
Cash and cash equivalents at beginning of period	803,632	632,784	530,631
Cash and cash equivalents at end of period	700,900	803,632	632,784
Cash payments for:
Interest, net of capitalized interest	39,963	7,061	0
Income taxes paid, net of refunds	(5,579)	95,933	89,104
Non-cash transactions:
Capital expenditures funded by capital lease borrowings	$ (31)	$ 0	$ (173)