CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018		Jun. 30, 2017
CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS
NET CASH PROVIDED BY OPERATING ACTIVITIES	$ 350,822		$ 331,783
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of marketable securities	(1,377,448)		(738,101)
Sales of marketable securities	1,407,623		665,246
Proceeds from the sale of aircraft, property and equipment			50,652
Acquisition of property and equipment:
Aircraft and rotable spare parts	(553,877)		(514,443)
Buildings and ground equipment	(19,070)		(2,420)
Aircraft deposits applied towards acquired aircraft			16,824
Increase in other assets	(4,962)		(6,098)
NET CASH USED IN INVESTING ACTIVITIES	(547,734)		(528,340)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of long-term debt	383,644		384,825
Principal payments on long-term debt	(160,387)		(169,550)
Net proceeds from issuance of common stock	2,320		1,783
Purchase of treasury stock and employee income tax paid on equity awards	(23,467)		(13,871)
Increase in debt issuance cost	(1,917)		(3,221)
Payment of cash dividends	(9,345)		(6,727)
NET CASH PROVIDED BY FINANCING ACTIVITIES	190,848		193,239
Decrease in cash and cash equivalents	(6,064)		(3,318)
Cash and cash equivalents at beginning of period	181,792	[1]	146,766
CASH AND CASH EQUIVALENTS AT END OF PERIOD	175,728		143,448
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Acquisition of rotable spare parts	426		2,038
Debt assumed on aircraft acquired off lease	59,132
Cash paid during the period for:
Interest, net of capitalized amounts	54,765		50,943
Income taxes	$ 1,852		$ 598

[1] Amounts adjusted due to the adoption of Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (Topic 606). See Note 1 to the financial statements contained in Part I, Item 1 of this report for additional information.