Property and Equipment (Narrative) (Details) - Flight Equipment [Member] - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Operating Leases, Future Minimum Payments Receivable [Abstract]
Minimum future lease payments, Due within next 12 months	$ 84,700	$ 142,300
Minimum future lease payments, Due within next 2 years	163,300	127,100
Minimum future lease payments, Due within next 3 years	157,500	124,300
Minimum future lease payments, Due within next 4 years	131,300	121,200
Minimum future lease payments, Due within next 5 years	88,200	87,100
Operating Leases, Future Minimum Payments Receivable, Thereafter	139,900	119,800
CAM [Member]
Property, Plant and Equipment [Line Items]
Leased aircraft, carrying value	$ 758,900	$ 803,700