CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
CONSOLIDATED STATEMENTS OF CASH FLOWS
NET CASH PROVIDED BY OPERATING ACTIVITIES	$ 532,289	$ 399,318
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of marketable securities	(1,002,624)	(2,160,567)
Sales of marketable securities	843,509	1,941,209
Proceeds from the sale of aircraft, property and equipment	51,079	1,848
Acquisition of property and equipment:
Aircraft and rotable spare parts	(563,524)	(619,805)
Deposits on aircraft	(46,733)
Buildings and ground equipment	(8,275)	(11,256)
Aircraft deposits applied towards acquired aircraft, net	36,533
Increase in other assets	(5,019)	(2,156)
NET CASH USED IN INVESTING ACTIVITIES	(695,054)	(850,727)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of long-term debt	384,825	497,510
Principal payments on long-term debt	(245,745)	(198,394)
Net proceeds from issuance of common stock	3,447	10,214
Purchase of treasury stock and cash tax withholding on shares issued	(14,330)
Increase in debt issuance cost	(3,245)	(4,520)
Payment of cash dividends	(10,868)	(6,669)
NET CASH PROVIDED BY FINANCING ACTIVITIES	114,084	298,141
Decrease in cash and cash equivalents	(48,681)	(153,268)
Cash and cash equivalents at beginning of period	146,766	203,035
CASH AND CASH EQUIVALENTS AT END OF PERIOD	98,085	49,767
Cash paid during the period for:
Interest, net of capitalized amounts	77,915	54,314
Income taxes	$ 2,354	$ 944