Summary of Significant Accounting Policies - Maintenance Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Amortization of heavy maintenance	$ 43,811	$ 43,111	$ 35,802
Deferred costs for heavy maintenance	35,400	9,100	33,600
Deferred heavy maintenance, gross	238,300	208,100
Accumulated heavy maintenance amortization	122,509	65,524
Airframe and Engine Maintenance Costs [Abstract]
Flight hour-based maintenance expense	48,471	41,818	35,675
Non-flight hour-based maintenance expense	50,116	38,630	38,281
Total maintenance, materials and repairs	98,587	80,448	$ 73,956
Heavy Maintenance
Property, Plant and Equipment [Line Items]
Accumulated heavy maintenance amortization	$ 162,800	$ 118,900