CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS
NET CASH PROVIDED BY OPERATING ACTIVITIES	$ 129,277	$ 109,347
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of marketable securities	(294,649)	(222,616)
Sales of marketable securities	344,682	219,362
Proceeds from the sale of equipment	102	630
Acquisition of property and equipment:
Aircraft and rotable spare parts	(44,469)	(27,555)
Deposits on aircraft	(24,200)
Buildings and ground equipment	(4,442)	(3,252)
Increase in other assets	(11,719)	(9,397)
NET CASH USED IN INVESTING ACTIVITIES	(34,695)	(42,828)
CASH FLOWS FROM FINANCING ACTIVITIES:
Principal payments on long-term debt	(85,971)	(84,598)
Tax benefit (deficiency) from exercise of common stock options	(175)	73
Net proceeds from issuance of common stock	2,666	2,161
Purchase of treasury stock	(196)	(897)
Payment of cash dividends	(4,132)	(4,070)
NET CASH USED IN FINANCING ACTIVITIES	(87,808)	(87,331)
Increase (decrease) in cash and cash equivalents	6,774	(20,812)
Cash and cash equivalents at beginning of period	133,772	129,526
CASH AND CASH EQUIVALENTS AT END OF PERIOD	140,546	108,714
Cash paid (received) during the year for:
Interest, net of capitalized amounts	36,633	39,261
Income taxes	$ 880	$ (1,477)