Income Taxes (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Taxes
Statutory Federal income tax rate (as a percent)	35.00%
Reconciliation between the statutory Federal income tax rate of 35% and the effective rate which is derived by dividing the provision for income taxes by income (loss) before provision for income taxes
Computed provision (benefit) for income taxes at the statutory rate	$ 68,013	$ (5,720)	$ 34,486
State income tax provision (benefit), net of federal income tax benefit	5,416	(107)	2,867
Non-deductible expenses	3,641	3,865	3,257
Valuation allowance changes affecting the provision for income taxes	(899)	5,981	1,430
Foreign income taxes, net of federal & state benefit		1,973
Other, net	334	1,819	(2,464)
Provision for income taxes	76,505	7,811	$ 39,576
Deferred tax assets:
Intangible Asset	30,369	34,819
Accrued benefits	47,514	43,853
Net operating loss carryforward	82,211	152,361
AMT credit carryforward	21,391	17,590
Deferred aircraft credits	55,544	53,797
Accrued reserves and other	24,575	27,008
Total deferred tax assets	261,604	329,428
Valuation allowance	(8,126)	(9,025)
Deferred tax liabilities:
Accelerated depreciation	(902,322)	(895,405)
Total deferred tax liabilities	(902,322)	(895,405)
Net deferred tax liability	$ 648,844	$ 575,002