CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS
NET CASH PROVIDED BY OPERATING ACTIVITIES	$ 269,483	$ 154,914
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of marketable securities	(236,527)	(498,113)
Sales of marketable securities	381,142	605,693
Proceeds from the sale of aircraft, property and equipment	1,366	43
Acquisition of property and equipment:
Aircraft and rotable spare parts	(73,482)	(197,341)
Buildings and ground equipment	(3,542)	(52,075)
Aircraft deposits applied towards acquired aircraft		4,660
Net cash received from sale of ExpressJet subsidiary		53,200
Decrease (increase) in other assets	(13,970)	7,028
NET CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES	54,987	(76,905)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of long-term debt		19,940
Principal payments on long-term debt	(89,796)	(98,204)
Net proceeds from issuance of common stock	1,532	2,261
Purchase of treasury and common stock and employee income tax paid on equity awards	(26,165)	(34,311)
Increase in debt issuance and lessor initial direct costs	(1,664)	(53)
Payment of cash dividends	(6,039)	(5,141)
NET CASH PROVIDED USED IN FINANCING ACTIVITIES	(122,132)	(115,508)
Increase (decrease) in cash and cash equivalents	202,338	(37,499)
Cash and cash equivalents at beginning of period	87,206	328,384
CASH AND CASH EQUIVALENTS AT END OF PERIOD	289,544	290,885
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Acquisition of rotable spare parts	34,100
Debt assumed on aircraft acquired under operating leases		14,475
Non-cash assets used to acquire aircraft under operating leases		150,688
Lease liability arising from the recognition of right-of-use asset		456,472
Cash paid during the period for:
Interest, net of capitalized amounts	31,413	34,288
Income taxes	$ 126	1,653
SUPPLEMENTAL DISCLOSURE OF SALE OF SUBSIDIARY:
Decrease in carrying amount of assets		(101,448)
Decrease in carrying amount of liabilities		68,341
Cash received from buyers		79,632
Gain on sale of subsidiary		$ 46,525