Property and Equipment (Schedule of Property and Equipment) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	$ 2,003,988	$ 1,731,983
Accumulated depreciation	(844,026)	(730,991)
Property and equipment, net	1,159,962	1,000,992
Flight Equipment [Member]
Property, Plant and Equipment [Line Items]
Operating Leases, Future Minimum Payments Receivable, Current	146,600
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	1,801,808	1,541,872
Operating Leases, Future Minimum Payments Receivable, in Two Years	111,000
Operating Leases, Future Minimum Payments Receivable, in Three Years	95,100
Operating Leases, Future Minimum Payments Receivable, in Four Years	76,600
Operating Leases, Future Minimum Payments Receivable, in Five Years	63,000
Ground equipment [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	53,523	49,229
facilities, leasehold improvements and office equipment [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	26,897	27,364
Construction in Progress [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	$ 121,760	$ 113,518