CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
CONSOLIDATED STATEMENTS OF CASH FLOWS
NET CASH PROVIDED BY OPERATING ACTIVITIES	$ 154,914	$ 165,895
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of marketable securities	(498,113)	(387,572)
Sales of marketable securities	605,693	496,945
Proceeds from the sale of aircraft, property and equipment	43
Acquisition of property and equipment:
Aircraft and rotable spare parts	(197,341)	(198,777)
Buildings and ground equipment	(52,075)	(9,305)
Aircraft deposits applied towards acquired aircraft	4,660
Net cash received from sale of ExpressJet subsidiary	53,200
Decrease (increase) in other assets	7,028	(1,364)
NET CASH USED IN INVESTING ACTIVITIES	(76,905)	(100,073)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of long-term debt	19,940	101,317
Principal payments on long-term debt	(98,204)	(71,587)
Net proceeds from issuance of common stock	2,261	2,320
Purchase of treasury stock and employee income tax paid on equity awards	(34,311)	(23,467)
Increase in debt issuance cost	(53)	(610)
Payment of cash dividends	(5,141)	(4,140)
NET CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES	(115,508)	3,833
Increase (decrease) in cash and cash equivalents	(37,499)	69,655
Cash and cash equivalents at beginning of period	328,384	181,792
CASH AND CASH EQUIVALENTS AT END OF PERIOD	290,885	251,447
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Acquisition of rotable spare parts		574
Debt assumed on aircraft acquired under operating leases	14,475	59,132
Right of use assets applied to aircraft acquired 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	34,288	26,481
Income taxes	1,653	$ 486
DETAILS OF SALES OF SUBSIDIARIES:
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 subsidiaries	$ 46,525