Operating Leases (Narrative) (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($) AircraftEngine	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) AircraftEngine	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Lessee Lease Description [Line Items]
Operating lease costs	$ 22,000	$ 22,100	$ 43,500	$ 44,100
Number of aircraft engines | AircraftEngine	32		32
Net book value of aircraft engines	$ 1,155,121		$ 1,155,121		$ 372,939
Lease income	$ 5,100		$ 13,300
Operating Lease, Income, Comprehensive Income [Extensible List]	us-gaap:OtherIncomeMember		us-gaap:OtherIncomeMember
Aircraft Engines [Member]
Lessee Lease Description [Line Items]
Net book value of aircraft engines	$ 306,500		$ 306,500