CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
CONSOLIDATED STATEMENTS OF CASH FLOWS
NET CASH PROVIDED BY OPERATING ACTIVITIES	$ 331,783	$ 228,034
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of marketable securities	(738,101)	(1,061,392)
Sales of marketable securities	665,246	1,071,668
Proceeds from the sale of aircraft, property and equipment	50,652
Acquisition of property and equipment:
Aircraft and rotable spare parts	(514,443)	(314,657)
Buildings and ground equipment	(2,420)	(7,303)
Aircraft deposits applied towards acquired aircraft, net	16,824
Increase in other assets	(6,098)	(1,499)
NET CASH USED IN INVESTING ACTIVITIES	(528,340)	(313,183)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of long-term debt	384,825	248,966
Principal payments on long-term debt	(169,550)	(136,328)
Net proceeds from issuance of common stock	1,783	4,048
Purchase of treasury stock	(13,871)
Increase in debt issuance cost	(3,221)	(2,495)
Payment of cash dividends	(6,727)	(4,095)
NET CASH PROVIDED BY FINANCING ACTIVITIES	193,239	110,096
Increase (decrease) in cash and cash equivalents	(3,318)	24,947
Cash and cash equivalents at beginning of period	146,766	203,035
CASH AND CASH EQUIVALENTS AT END OF PERIOD	143,448	227,982
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Acquisition of rotable spare parts	2,038
Cash paid during the period for:
Interest, net of capitalized amounts	50,943	35,887
Income taxes	$ 598	$ 741