Fixed Assets (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) Air_craft	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Property Plant And Equipment [Abstract]
Depreciation and amortization	$ 27,896	$ 32,495	$ 43,147
Number of Aircraft engines | Air_craft	23
Aircraft engines with a net book value	$ 211,100