Property and Equipment (Schedule of Property and Equipment) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	$ 2,801,305	$ 2,501,489
Accumulated depreciation	(1,093,973)	(946,484)
Property and equipment, net	1,707,332	1,555,005
Flight Equipment [Member]
Property, Plant and Equipment [Line Items]
Operating Leases, Future Minimum Payments Receivable, Current	45,900	142,300
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	2,465,193	2,340,840
Operating Leases, Future Minimum Payments Receivable, in Two Years	169,600	127,100
Operating Leases, Future Minimum Payments Receivable, in Three Years	163,700	124,300
Operating Leases, Future Minimum Payments Receivable, in Four Years	137,500	121,200
Operating Leases, Future Minimum Payments Receivable, in Five Years	94,400	87,100
Ground equipment [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	59,291	57,455
facilities, leasehold improvements and office equipment [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	32,207	28,745
Construction in Progress [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	$ 244,614	$ 74,449