Condensed Statements Of Cash Flows (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating activities:
Net income	$ (44,922)	$ 31,261
Adjustments to reconcile net income to net cash provided by operations:
Losses reclassified from other comprehensive income	79	84
Stock-based compensation	3,075	2,816
Allowance for doubtful accounts (recoveries)	(7)	(30)
Amortization of deferred gains and losses and debt issuance costs	1,624	3,351
Depreciation and amortization	39,373	31,509
Deferred income tax expense (benefit)	(20,266)	19,474
Loss on disposal of assets	848	1,105
Lease termination costs	0	4,776
Special charges, non-operating	9,201	0
Changes in operating assets and liabilities:
Accounts receivable	(2,983)	(7,526)
Aircraft maintenance deposits, net	14,844	(12,774)
Prepaid income taxes	0	(846)
Long-term deposits and other assets	3,512	(13,559)
Deferred heavy maintenance	(50,712)	(9,558)
Accounts payable	6,227	18,937
Air traffic liability	93,483	104,285
Other liabilities	117,779	(382)
Other	(20)	115
Net cash provided by operating activities	171,135	173,038
Investing activities:
Purchase of available-for-sale investment securities	(30,853)	(24,490)
Proceeds from the maturity of available-for-sale investment securities	30,504	24,219
Pre-delivery deposits for flight equipment, net of refunds	(41,580)	(44,752)
Capitalized interest	(1,500)	(1,647)
Purchase of property and equipment	(237,221)	(111,141)
Net cash used in investing activities	(280,650)	(157,811)
Financing activities:
Proceeds from issuance of long-term debt	227,128	115,526
Proceeds from stock options exercised	2	0
Payments on debt and capital lease obligations	(18,847)	(10,235)
Repurchase of common stock	(959)	(1,034)
Debt issuance costs	(201)	(2,274)
Net cash provided by financing activities	207,123	101,983
Net (decrease) increase in cash and cash equivalents	97,608	117,210
Cash and cash equivalents at beginning of period	800,849	700,900
Cash and cash equivalents at end of period	898,457	818,110
Cash payments for:
Interest, net of capitalized interest	8,569	3,943
Income taxes paid, net of refunds	679	2,881
Non-cash transactions:
Capital expenditures funded by capital lease borrowings	$ (237,042)	$ (130)