Fixed Assets (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) Air_craft	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Property Plant And Equipment [Abstract]
Depreciation and amortization	$ 38,369	$ 27,896	$ 32,495
Number of Aircraft engines | Air_craft	14
Aircraft engines with a net book value	$ 200,400
Lease income	$ 20,900
Operating Lease, Income, Comprehensive Income [Extensible List]	us-gaap:OtherIncomeMember