Operating Leases (Narrative) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) AircraftEngine	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Lessee Lease Description [Line Items]
Operating lease costs	$ 21,000	$ 21,900
Number of aircraft engines | AircraftEngine	29
Net book value of aircraft engines	$ 1,077,891		$ 372,939
Lease income	$ 8,200
Operating Lease, Income, Comprehensive Income [Extensible List]	us-gaap:OtherIncomeMember
Aircraft Engines [Member]
Lessee Lease Description [Line Items]
Net book value of aircraft engines	$ 286,000