Summary of Significant Accounting Policies - Maintenance Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Deferred costs for heavy maintenance	$ 176,000	$ 190,500	$ 78,200
Deferred heavy maintenance, gross	504,200	366,300
Accumulated heavy maintenance amortization	492,447	332,864
Airframe and Engine Maintenance Costs [Abstract]
Total maintenance, materials and repairs	143,575	129,078	110,439
Heavy maintenance and major overhaul
Property, Plant and Equipment [Line Items]
Amortization of heavy maintenance	63,364	41,286	53,855
Heavy Maintenance
Property, Plant and Equipment [Line Items]
Accumulated heavy maintenance amortization	142,600	117,300
Flight hour-based maintenance expense
Airframe and Engine Maintenance Costs [Abstract]
Total maintenance, materials and repairs	78,253	68,039	54,802
Non-flight hour-based maintenance expense
Airframe and Engine Maintenance Costs [Abstract]
Total maintenance, materials and repairs	$ 65,322	$ 61,039	$ 55,637