Property and Equipment (Narrative) (Details) - Flight Equipment [Member] - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Operating Leases, Future Minimum Payments Receivable [Abstract]
Minimum future lease payments, Due within next 12 months	$ 124,158	$ 142,319
Minimum future lease payments, Due within next 2 years	156,008	127,097
Minimum future lease payments, Due within next 3 years	150,153	124,267
Minimum future lease payments, Due within next 4 years	124,667	121,226
Minimum future lease payments, Due within next 5 years	84,843	87,098
Operating Leases, Future Minimum Payments Receivable, Thereafter	121,467	119,761
CAM [Member]
Property, Plant and Equipment [Line Items]
Leased aircraft, carrying value	$ 782,900	$ 803,700