Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating activities:
Net income	$ 335,255	$ 155,749	$ 415,522
Adjustments to reconcile net income to net cash provided by operations:
Losses reclassified from other comprehensive income	315	315	335
Share-based compensation	8,154	11,021	8,522
Allowance for doubtful accounts (recoveries)	0	(11)	(53)
Amortization of deferred gains, losses and debt issuance costs	8,654	8,819	7,944
Depreciation and amortization	225,264	176,727	140,152
Deferred income tax expense (benefit)	115,689	46,303	(492)
Loss on disposal of assets	17,350	9,580	4,168
Lease termination costs	0	0	12,629
Special charges, non-operating	0	90,357	0
Changes in operating assets and liabilities:
Accounts receivable, net	(26,147)	1,674	(8,134)
Aircraft maintenance deposits, net	22,453	14,019	(37,930)
Other assets	14,999	(4,803)	(50,951)
Deferred heavy maintenance, net	(175,957)	(190,381)	(78,237)
Income tax receivable	(21,013)	69,844	(69,844)
Prepaid income taxes	1,431	0	0
Accounts payable	569	15,317	6,030
Air traffic liability	23,429	28,270	43,527
Other liabilities	(140,402)	74,038	31,672
Other	(822)	(375)	380
Net cash provided by operating activities	409,221	506,463	425,240
Investing activities:
Purchase of available-for-sale investment securities	(122,410)	(124,430)	(107,246)
Proceeds from the maturity and sale of available-for-sale investment securities	120,830	122,947	105,906
Proceeds from sale of property and equipment	0	11,400	0
Pre-delivery deposits on flight equipment, net of refunds	(102,102)	(177,424)	(149,477)
Capitalized interest	(10,774)	(8,729)	(12,305)
Assets under construction for others	(7,936)	(501)	0
Purchase of property and equipment	(192,437)	(606,971)	(628,881)
Net cash used in investing activities	(314,829)	(783,708)	(792,003)
Financing activities:
Proceeds from issuance of long-term debt	225,891	832,099	629,725
Proceeds from stock options exercised	1	51	45
Payments on debt obligations	(246,783)	(137,275)	(102,313)
Payments on finance lease obligations	(96,547)	(205,720)	(425)
Reimbursement for assets under construction for others	5,618	501	0
Repurchase of common stock	(5,439)	(1,162)	(46,580)
Debt issuance costs	(2,909)	(7,365)	(13,740)
Net cash (used in) provided by financing activities	(120,168)	481,129	466,712
Net increase (decrease) in cash and cash equivalents	(25,776)	203,884	99,949
Cash and cash equivalents at beginning of period	1,004,733	800,849	700,900
Cash and cash equivalents at end of period	978,957	1,004,733	800,849
Cash payments for:
Interest, net of capitalized interest	80,254	65,123	37,902
Income taxes paid (received), net	5,843	(73,489)	5,826
Operating cash flows for operating leases (1)	191,004
Financing cash flows for finance leases (1)	674
Non-cash transactions:
Capital expenditures funded by finance lease borrowings	45,608	$ 987	$ 1,370
Capital expenditures funded by operating lease borrowings (1)	$ 569,948