Employee Benefit Plans - Germany & UK (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension plans
Plan assets	$ 75,875	$ 62,952	$ 64,886
Weighted average expected long-term rate	3.86%
German Pension Plan | Unfunded Plan
Pension plans
Plan assets	$ 0
German Pension Plan | Unfunded Plan | Minimum
Pension plans
Qualifying period	10 years
U.K. Pension Plan
Pension plans
Weighted average expected long-term rate	3.87%	4.25%
U.K. Pension Plan | Minimum
Pension plans
Minimum required years prior to retirement for eligibility	3 years
Historical performance period	15 years	10 years
U.K. Pension Plan | Maximum
Pension plans
Historical performance period	20 years	20 years
Asterion Pension Plan
Pension plans
Weighted average expected long-term rate	1.10%	1.80%
Asterion Pension Plan | Minimum
Pension plans
Minimum required years prior to retirement for eligibility	3 years
Norway Pension Plan
Pension plans
Weighted average expected long-term rate	3.80%	4.30%
Norway Pension Plan | Minimum
Pension plans
Minimum required years prior to retirement for eligibility	3 years
Historical performance period	10 years
Norway Pension Plan | Maximum
Pension plans
Historical performance period	20 years