Fixed Assets (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) Air_craft	Dec. 31, 2018 USD ($)
Property Plant And Equipment [Abstract]
Depreciation and amortization	$ 40,863	$ 38,369	$ 27,896
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