Commitments and Contingencies (Details) € in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017 EUR (€)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Commitment and Contingencies
Operating leases term, low end of range	1 year	1 year
Operating leases term, high end of range	5 years	5 years
Total lease and rent expense		$ 2,359	$ 2,659	$ 2,307
Foreign exchange hedges assets		111
Foreign exchange hedges liabilities			352
Future minimum payments under operating leases
2018		1,658
2019		1,306
2020		1,012
2021		815
2022		148
Thereafter		0
Prepaid Expenses and Other Current Assets
Commitment and Contingencies
Foreign exchange hedges assets		83
Other Assets
Commitment and Contingencies
Foreign exchange hedges assets		28
Accrued Expenses
Commitment and Contingencies
Foreign exchange hedges liabilities			309
Other liabilities
Commitment and Contingencies
Foreign exchange hedges liabilities			$ 43
Equipment and Construction Contracts
Commitment and Contingencies
Purchase commitment	€ 3,692	$ 14,703