Other Current Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepayments to suppliers	$ 5,671	$ 5,109
Other debtors	2,809	4,225
Prepaid expenses	8,437	7,891
Derivative instruments	389	0
Gross book value at end of period	17,306	17,225
Net book value at end of period	$ 17,306	$ 17,225