Property and Equipment (Schedule of Property and Equipment) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	$ 2,572,441	$ 2,501,489
Accumulated depreciation	(1,002,601)	(946,484)
Property and equipment, net	1,569,840	1,555,005
Flight Equipment [Member]
Property, Plant and Equipment [Line Items]
Operating Leases, Future Minimum Payments Receivable, Current	124,158	142,319
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	2,375,190	2,340,840
Operating Leases, Future Minimum Payments Receivable, in Two Years	156,008	127,097
Operating Leases, Future Minimum Payments Receivable, in Three Years	150,153	124,267
Operating Leases, Future Minimum Payments Receivable, in Four Years	124,667	121,226
Operating Leases, Future Minimum Payments Receivable, in Five Years	84,843	87,098
Ground equipment [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	59,803	57,455
facilities, leasehold improvements and office equipment [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	29,365	28,745
Construction in Progress [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	$ 108,083	$ 74,449