Condensed Consolidating Financial Information - Condensed Consolidating Statements of Cash Flows (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Condensed Consolidating Statements of Cash Flows
Net Cash Provided By Operating Activities	$ 3,458	$ 311,212
Cash Flows From Investing Activities:
Net payments to affiliates	0	0
Additions to property and equipment, including pre-delivery deposits	(93,956)	(151,577)
Proceeds from the sale and sale leaseback of aircraft and aircraft related equipment		4,350
Purchases of investments	(64,215)	(189,929)
Sales of investments	143,679	225,706
Other	0	(6,275)
Net cash used in investing activities	(14,492)	(117,725)
Cash Flows From Financing Activities:
Long-term borrowings	283,964	0
Repayments of long-term debt and finance lease obligations	(39,129)	(77,471)
Debt issuance costs	0	(33)
Dividend payments	(5,514)	(11,554)
Net payments from affiliates	0	0
Repurchases of common stock	(7,510)	(30,690)
Other	(1,313)	(1,012)
Net cash provided by (used in) financing activities	230,498	(120,760)
Net increase in cash and cash equivalents	219,464	72,727
Cash, cash equivalents, and restricted cash - Beginning of Period	373,056	268,577
Cash, cash equivalents, and restricted cash - End of Period	592,520	341,304
Eliminations
Condensed Consolidating Statements of Cash Flows
Net Cash Provided By Operating Activities	0	0
Cash Flows From Investing Activities:
Net payments to affiliates	26,677	57,305
Additions to property and equipment, including pre-delivery deposits	0	0
Proceeds from the sale and sale leaseback of aircraft and aircraft related equipment		0
Purchases of investments	0	0
Sales of investments	0	0
Other		0
Net cash used in investing activities	26,677	57,305
Cash Flows From Financing Activities:
Long-term borrowings	0
Repayments of long-term debt and finance lease obligations	0	0
Debt issuance costs		0
Dividend payments	0	0
Net payments from affiliates	(26,677)	(57,305)
Repurchases of common stock	0	0
Other	0	0
Net cash provided by (used in) financing activities	(26,677)	(57,305)
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 Operating Activities	4,693	(956)
Cash Flows From Investing Activities:
Net payments to affiliates	(9,650)	(7,600)
Additions to property and equipment, including pre-delivery deposits	0	0
Proceeds from the sale and sale leaseback of aircraft and aircraft related equipment		0
Purchases of investments	0	0
Sales of investments	0	0
Other		0
Net cash used in investing activities	(9,650)	(7,600)
Cash Flows From Financing Activities:
Long-term borrowings	0
Repayments of long-term debt and finance lease obligations	0	0
Debt issuance costs		0
Dividend payments	(5,514)	(11,554)
Net payments from affiliates	17,027	49,705
Repurchases of common stock	(7,510)	(30,690)
Other	0	0
Net cash provided by (used in) financing activities	4,003	7,461
Net increase in cash and cash equivalents	(954)	(1,095)
Cash, cash equivalents, and restricted cash - Beginning of Period	1,228	5,154
Cash, cash equivalents, and restricted cash - End of Period	274	4,059
Subsidiary Issuer / Guarantor | Reportable Legal Entities
Condensed Consolidating Statements of Cash Flows
Net Cash Provided By Operating Activities	726	314,741
Cash Flows From Investing Activities:
Net payments to affiliates	(16,961)	(49,705)
Additions to property and equipment, including pre-delivery deposits	(86,936)	(147,116)
Proceeds from the sale and sale leaseback of aircraft and aircraft related equipment		4,350
Purchases of investments	(64,215)	(189,929)
Sales of investments	143,679	225,706
Other		(6,275)
Net cash used in investing activities	(24,433)	(162,969)
Cash Flows From Financing Activities:
Long-term borrowings	283,964
Repayments of long-term debt and finance lease obligations	(39,129)	(77,465)
Debt issuance costs		(33)
Dividend payments	0	0
Net payments from affiliates	0	0
Repurchases of common stock	0	0
Other	(1,313)	(1,012)
Net cash provided by (used in) financing activities	243,522	(78,510)
Net increase in cash and cash equivalents	219,815	73,262
Cash, cash equivalents, and restricted cash - Beginning of Period	362,933	255,279
Cash, cash equivalents, and restricted cash - End of Period	582,748	328,541
Non-Guarantor Subsidiaries | Reportable Legal Entities
Condensed Consolidating Statements of Cash Flows
Net Cash Provided By Operating Activities	(1,961)	(2,573)
Cash Flows From Investing Activities:
Net payments to affiliates	(66)	0
Additions to property and equipment, including pre-delivery deposits	(7,020)	(4,461)
Proceeds from the sale and sale leaseback of aircraft and aircraft related equipment		0
Purchases of investments	0	0
Sales of investments	0	0
Other		0
Net cash used in investing activities	(7,086)	(4,461)
Cash Flows From Financing Activities:
Long-term borrowings	0
Repayments of long-term debt and finance lease obligations	0	(6)
Debt issuance costs		0
Dividend payments	0	0
Net payments from affiliates	9,650	7,600
Repurchases of common stock	0	0
Other	0	0
Net cash provided by (used in) financing activities	9,650	7,594
Net increase in cash and cash equivalents	603	560
Cash, cash equivalents, and restricted cash - Beginning of Period	8,895	8,144
Cash, cash equivalents, and restricted cash - End of Period	$ 9,498	$ 8,704