Condensed Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Operating activities:
Net income (loss)	$ 170,577	$ (33,668)
Adjustments to reconcile net income to net cash provided by operations:
Losses reclassified from other comprehensive income	(148)	(159)
Share-based compensation	6,413	5,381
Allowance for doubtful accounts (recoveries)	0	(12)
Amortization of deferred gains and losses and debt issuance costs	4,365	4,552
Depreciation and amortization	105,639	84,991
Deferred income tax expense (benefit)	44,511	(17,604)
Loss on disposal of assets	3,463	5,492
Special charges, non-operating	0	88,613
Changes in operating assets and liabilities:
Accounts receivable	(30,465)	(9,212)
Aircraft maintenance deposits, net	(6,214)	11,222
Prepaid income taxes	(1,962)	0
Long-term deposits and other assets	10,212	3,003
Deferred heavy maintenance, net	(88,350)	(94,267)
Income tax receivable	0	828
Accounts payable	2,024	25,413
Air traffic liability	111,009	93,936
Other liabilities	6,154	83,809
Other	(424)	8
Net cash provided by operating activities	341,024	250,988
Investing activities:
Purchase of available-for-sale investment securities	(57,355)	(73,687)
Proceeds from the maturity of available-for-sale investment securities	56,595	72,964
Proceeds from sale of property and equipment	0	9,500
Pre-delivery deposits on flight equipment, net of refunds	(75,826)	(92,205)
Capitalized interest	(4,936)	(4,178)
Assets under construction for others	(2,235)	0
Purchase of property and equipment	(154,702)	(323,229)
Net cash used in investing activities	(238,459)	(410,835)
Financing activities:
Proceeds from issuance of long-term debt	94,706	440,340
Proceeds from stock options exercised	1	2
Payments on debt obligations	(85,785)	(60,649)
Payments on finance lease obligations	(1,796)	(205,403)
Reimbursement for assets under construction for others	2,235	0
Repurchase of common stock	(5,248)	(986)
Debt issuance costs	(614)	(1,944)
Net cash provided by financing activities	3,499	171,360
Net increase in cash and cash equivalents	106,064	11,513
Cash and cash equivalents at beginning of period	1,004,733	800,849
Cash and cash equivalents at end of period	1,110,797	812,362
Cash payments for:
Interest, net of capitalized interest	41,279	16,769
Income taxes paid, net of refunds	7,394	3,270
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows for operating leases	95,643	0
Operating cash flows for finance leases	1,457	0
Financing cash flows for finance leases	339	0
Non-cash transactions:
Capital expenditures funded by finance lease borrowings	96,371	315
Capital expenditures funded by operating lease borrowings	$ 159,548	$ 0