Restructuring Costs - Severance Obligation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
2019 French Restructuring Obligation
Restructuring Reserve [Roll Forward]
Beginning balance of accrued costs	$ 1,922	$ 0
Payments	(1,813)	(2,441)
Foreign currency impact	(33)	24
Ending balance of accrued costs	248	1,922
2019 Corporate Restructuring Obligations
Restructuring Reserve [Roll Forward]
Beginning balance of accrued costs	1,080	0
Payments	(1,014)	(2,326)
Ending balance of accrued costs	272	1,080
Employee Severance | 2019 French Restructuring Obligation
Restructuring Reserve [Roll Forward]
Charges for employee severance, benefits and other costs	172	4,339
Employee Severance | 2019 Corporate Restructuring Obligations
Restructuring Reserve [Roll Forward]
Charges for employee severance, benefits and other costs	$ 206	$ 3,406