Property and Equipment (Schedule of Property and Equipment) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	$ 3,110,527	$ 2,912,217
Accumulated depreciation	(1,205,587)	(1,146,197)
Property and equipment, net	1,904,940	1,766,020
Flight Equipment [Member]
Property, Plant and Equipment [Line Items]
Operating Leases, Future Minimum Payments Receivable, Current	54,900	186,800
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	2,743,232	2,598,113
Operating Leases, Future Minimum Payments Receivable, in Two Years	213,000	178,200
Operating Leases, Future Minimum Payments Receivable, in Three Years	185,000	152,000
Operating Leases, Future Minimum Payments Receivable, in Four Years	142,700	110,100
Operating Leases, Future Minimum Payments Receivable, in Five Years	108,200	75,500
Ground equipment [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	63,697	59,628
facilities, leasehold improvements and office equipment [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	35,635	33,649
Construction in Progress [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	$ 267,963	$ 220,827