Income Taxes - Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
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 income taxes
Computed provision (benefit) for income taxes at the statutory rate	$ (87,084)	$ 68,013	$ (5,720)
State income tax provision (benefit), net of federal income tax benefit	(5,768)	5,416	(107)
Non-deductible expenses	3,552	3,641	3,865
Valuation allowance changes affecting the provision for income taxes	751	(899)	5,981
Foreign income taxes, net of federal & state benefit			1,973
Other, net	1,323	334	1,819
Provision for income taxes	(87,226)	76,505	$ 7,811
Deferred tax assets:
Intangible Asset	4,983	30,369
Accrued benefits	48,482	47,514
Net operating loss carryforward	286,389	82,211
AMT credit carryforward	17,589	21,391
Deferred aircraft credits	60,415	55,544
Accrued reserves and other	47,906	24,575
Total deferred tax assets	465,764	261,604
Valuation allowance	(8,877)	(8,126)
Deferred tax liabilities:
Accelerated depreciation	(1,022,291)	(902,322)
Total deferred tax liabilities	(1,022,291)	(902,322)
Net deferred tax liability	$ 565,404	$ 648,844