Condensed Consolidating Financial Information - Condensed Consolidating Statements of Cash Flows (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Condensed Consolidating Statements of Cash Flows
Net Cash Provided By (Used In) Operating Activities	$ (173,482)	$ 456,895
Cash Flows From Investing Activities:
Net payments to affiliates	0	0
Additions to property and equipment, including pre-delivery deposits	(101,775)	(280,288)
Proceeds from the purchase assignment and sale leaseback	114,000	0
Proceeds from the disposition of aircraft related equipment	0	9,045
Purchases of investments	(408,955)	(265,705)
Sales of investments	214,469	267,464
Other	0	(6,275)
Net cash used in investing activities	(182,261)	(275,759)
Cash Flows From Financing Activities:
Long-term borrowings	602,264	227,889
Repayments of long-term debt and finance lease obligations	(64,686)	(95,356)
Debt issuance costs	(3,506)	(1,162)
Dividend payments	(5,514)	(17,206)
Net payments from affiliates	0	0
Repurchases of common stock	(7,510)	(50,690)
Other	(1,359)	(1,026)
Net cash provided by financing activities	519,689	62,449
Net increase in cash and cash equivalents	163,946	243,585
Cash, cash equivalents, and restricted cash - Beginning of Period	373,056	268,577
Cash, cash equivalents, and restricted cash - End of Period	537,002	512,162
Eliminations
Condensed Consolidating Statements of Cash Flows
Net Cash Provided By (Used In) Operating Activities	0	0
Cash Flows From Investing Activities:
Net payments to affiliates	32,837	85,623
Additions to property and equipment, including pre-delivery deposits	0	0
Proceeds from the purchase assignment and sale leaseback	0
Proceeds from the disposition of aircraft related equipment		0
Purchases of investments	0	0
Sales of investments	0	0
Other		0
Net cash used in investing activities	32,837	85,623
Cash Flows From Financing Activities:
Long-term borrowings	0	0
Repayments of long-term debt and finance lease obligations	0	0
Debt issuance costs	0	0
Dividend payments	0	0
Net payments from affiliates	(32,837)	(85,623)
Repurchases of common stock	0	0
Other	0	0
Net cash provided by financing activities	(32,837)	(85,623)
Net increase in cash and cash equivalents	0	0
Cash, cash equivalents, and restricted cash - Beginning of Period	0	0
Cash, cash equivalents, and restricted cash - End of Period	0	0
Parent Issuer / Guarantor | Reportable legal entities
Condensed Consolidating Statements of Cash Flows
Net Cash Provided By (Used In) Operating Activities	4,111	(587)
Cash Flows From Investing Activities:
Net payments to affiliates	(7,850)	(10,350)
Additions to property and equipment, including pre-delivery deposits	0	0
Proceeds from the purchase assignment and sale leaseback	0
Proceeds from the disposition of aircraft related equipment		0
Purchases of investments	0	0
Sales of investments	0	0
Other		0
Net cash used in investing activities	(7,850)	(10,350)
Cash Flows From Financing Activities:
Long-term borrowings	0	0
Repayments of long-term debt and finance lease obligations	0	0
Debt issuance costs	0	0
Dividend payments	(5,514)	(17,206)
Net payments from affiliates	24,987	75,273
Repurchases of common stock	(7,510)	(50,690)
Other	0	0
Net cash provided by financing activities	11,963	7,377
Net increase in cash and cash equivalents	8,224	(3,560)
Cash, cash equivalents, and restricted cash - Beginning of Period	1,228	5,154
Cash, cash equivalents, and restricted cash - End of Period	9,452	1,594
Subsidiary Issuer / Guarantor | Reportable legal entities
Condensed Consolidating Statements of Cash Flows
Net Cash Provided By (Used In) Operating Activities	(177,272)	462,734
Cash Flows From Investing Activities:
Net payments to affiliates	(24,921)	(75,273)
Additions to property and equipment, including pre-delivery deposits	(94,565)	(274,786)
Proceeds from the purchase assignment and sale leaseback	114,000
Proceeds from the disposition of aircraft related equipment		9,045
Purchases of investments	(408,955)	(265,705)
Sales of investments	214,469	267,464
Other		(6,275)
Net cash used in investing activities	(199,972)	(345,530)
Cash Flows From Financing Activities:
Long-term borrowings	602,264	227,889
Repayments of long-term debt and finance lease obligations	(64,686)	(95,350)
Debt issuance costs	(3,506)	(1,162)
Dividend payments	0	0
Net payments from affiliates	0	0
Repurchases of common stock	0	0
Other	(1,359)	(1,026)
Net cash provided by financing activities	532,713	130,351
Net increase in cash and cash equivalents	155,469	247,555
Cash, cash equivalents, and restricted cash - Beginning of Period	362,933	255,279
Cash, cash equivalents, and restricted cash - End of Period	518,402	502,834
Non-Guarantor Subsidiaries | Reportable legal entities
Condensed Consolidating Statements of Cash Flows
Net Cash Provided By (Used In) Operating Activities	(321)	(5,252)
Cash Flows From Investing Activities:
Net payments to affiliates	(66)	0
Additions to property and equipment, including pre-delivery deposits	(7,210)	(5,502)
Proceeds from the purchase assignment and sale leaseback	0
Proceeds from the disposition of aircraft related equipment		0
Purchases of investments	0	0
Sales of investments	0	0
Other		0
Net cash used in investing activities	(7,276)	(5,502)
Cash Flows From Financing Activities:
Long-term borrowings	0	0
Repayments of long-term debt and finance lease obligations	0	(6)
Debt issuance costs	0	0
Dividend payments	0	0
Net payments from affiliates	7,850	10,350
Repurchases of common stock	0	0
Other	0	0
Net cash provided by financing activities	7,850	10,344
Net increase in cash and cash equivalents	253	(410)
Cash, cash equivalents, and restricted cash - Beginning of Period	8,895	8,144
Cash, cash equivalents, and restricted cash - End of Period	$ 9,148	$ 7,734