Property and Equipment (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Leases, Future Minimum Payments Receivable [Abstract]
Asset Impairment Charges	$ (39,100)	$ 39,075	$ 0	$ 0
Flight Equipment [Member]
Operating Leases, Future Minimum Payments Receivable [Abstract]
Minimum future lease payments, Due within next 12 months		222,400
Minimum future lease payments, Due within next 2 years		195,500
Minimum future lease payments, Due within next 3 years		150,500
Minimum future lease payments, Due within next 4 years		99,800
Minimum future lease payments, Due within next 5 years		90,700
CAM [Member] | Flight Equipment [Member]
Property, Plant and Equipment [Line Items]
Leased aircraft, carrying value		$ 1,097,600	$ 889,300