Consolidated Statements of Cash Flows - USD ($)		12 Months Ended
		Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Operating activities:
Net income (loss)		$ (428,700,000)		$ 335,255,000		$ 155,749,000
Adjustments to reconcile net income (loss) to net cash provided by operations:
Losses reclassified from other comprehensive income		252,000		315,000		315,000
Share-based compensation		11,575,000		8,154,000		11,021,000
Allowance for doubtful accounts (recoveries)		(249,000)		0		(11,000)
Amortization of debt issuance costs		10,752,000		8,654,000		8,819,000
Depreciation and amortization		278,588,000		225,264,000		176,727,000
Accretion expense		10,138,000		0		0
Deferred income tax expense (benefit)		(46,086,000)		115,689,000		46,303,000
Loss on disposal of assets		2,264,000		17,350,000		9,580,000
Special charges, non-operating		0		0		90,357,000
Changes in operating assets and liabilities:
Accounts receivable, net		30,486,000		(26,147,000)		1,674,000
Aircraft maintenance deposits, net		23,732,000		22,453,000		14,019,000
Deposits and other assets		(12,944,000)		14,999,000		(4,803,000)
Deferred heavy maintenance, net		(75,230,000)		(175,957,000)		(190,381,000)
Income tax receivable		(126,447,000)		(21,013,000)		69,844,000
Prepaid income taxes		(223,000)		1,431,000		0
Accounts payable		(17,052,000)		569,000		15,317,000
Air traffic liability		86,558,000		23,429,000		28,270,000
Other liabilities		27,194,000		1,698,000		74,038,000
Other		118,000		(822,000)		(375,000)
Net cash provided (used) by operating activities		(225,274,000)		551,321,000		506,463,000
Investing activities:
Purchase of available-for-sale investment securities		(118,893,000)		(122,410,000)		(124,430,000)
Proceeds from the maturity and sale of available-for-sale investment securities		117,665,000		120,830,000		122,947,000
Proceeds from sale of property and equipment		0		0		11,400,000
Pre-delivery deposits on flight equipment, net of refunds		(143,220,000)		(102,102,000)		(177,424,000)
Capitalized interest		(12,233,000)		(10,774,000)		(8,729,000)
Assets under construction for others		(3,944,000)		(7,936,000)		(501,000)
Purchase of property and equipment		(393,375,000)		(334,537,000)		(606,971,000)
Net cash used in investing activities		(554,000,000)		(456,929,000)		(783,708,000)
Financing activities:
Proceeds from issuance of long-term debt		1,612,391,000		225,891,000		832,099,000
Proceeds from issuance of common stock and warrants		366,783,000		0		0
Proceeds from stock options exercised		39,000		1,000		51,000
Payments on debt obligations		(254,304,000)		(246,783,000)		(137,275,000)
Payments on finance lease obligations		(25,401,000)		(96,547,000)		(205,720,000)
Reimbursement for assets under construction for others		4,153,000		5,618,000		501,000
Repurchase of common stock		(1,669,000)		(5,439,000)		(1,162,000)
Debt and equity issuance costs		(40,551,000)		(2,909,000)		(7,365,000)
Net cash provided (used) by financing activities		1,661,441,000		(120,168,000)		481,129,000
Net increase (decrease) in cash, cash equivalents, and restricted cash		882,167,000		(25,776,000)		203,884,000
Cash and cash equivalents at beginning of period		978,957,000	[1]	1,004,733,000	[1]	800,849,000
Cash and cash equivalents at the end of period	[1]	1,861,124,000		978,957,000		1,004,733,000
Cash payments for:
Interest, net of capitalized interest		80,837,000		80,254,000		65,123,000
Income taxes paid (received), net		(17,790,000)		5,843,000		(73,489,000)
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows for operating leases	[2]	180,805,000		191,004,000
Financing cash flows for finance leases	[2]	194,000		674,000
Non-cash transactions:
Capital expenditures funded by finance lease borrowings		565,000		45,608,000		987,000
Capital expenditures funded by operating lease borrowings	[2]	$ 168,526,000		$ 569,948,000		$ 0

[1] The sum of cash and cash equivalents and restricted cash on our consolidated balance sheets equals cash, cash equivalents, and restricted cash in our statement of cash flows.

[2] The Company adopted ASU No. 2016-02, "Leases (Topic 842)," utilizing the modified retrospective adoption method with an effective date of January 1, 2019. Therefore, the consolidated financial statements for 2020 and 2019 are presented under the new standard, while 2018 is not adjusted and continues to be reported in accordance with the Company's historical accounting policy.