CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018		Sep. 30, 2017
CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS
NET CASH PROVIDED BY OPERATING ACTIVITIES	$ 573,127		$ 532,289
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of marketable securities	(1,575,991)		(1,002,624)
Sales of marketable securities	1,699,284		843,509
Proceeds from the sale of aircraft, property and equipment			51,079
Acquisition of property and equipment:
Aircraft and rotable spare parts	(848,723)		(563,524)
Deposits on aircraft			(46,733)
Buildings and ground equipment	(35,870)		(8,275)
Aircraft deposits applied towards acquired aircraft	21,421		36,533
Increase in other assets	(2,479)		(5,019)
NET CASH USED IN INVESTING ACTIVITIES	(742,358)		(695,054)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of long-term debt	626,163		384,825
Principal payments on long-term debt	(262,923)		(245,745)
Net proceeds from issuance of common stock	5,212		3,447
Purchase of treasury stock and employee income tax paid on equity awards	(38,720)		(14,330)
Increase in debt issuance cost	(3,182)		(3,245)
Payment of cash dividends	(14,550)		(10,868)
NET CASH PROVIDED BY FINANCING ACTIVITIES	312,000		114,084
Increase (decrease) in cash and cash equivalents	142,769		(48,681)
Cash and cash equivalents at beginning of period	181,792	[1]	146,766
CASH AND CASH EQUIVALENTS AT END OF PERIOD	324,561		98,085
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Acquisition of rotable spare parts	10,346
Debt assumed on aircraft acquired off lease	59,132
Cash paid during the period for:
Interest, net of capitalized amounts	85,611		77,915
Income taxes	$ 2,382		$ 2,354

[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.