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Commitments and Contingencies (Details) $ in Thousands, € in Millions	12 Months Ended
	Dec. 31, 2018 EUR (€)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 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		$ 2,260	$ 2,359	$ 2,659
Foreign exchange hedges assets			111
Foreign exchange hedges liabilities		16
Future minimum payments under operating leases
2019		1,319
2020		1,030
2021		720
2022		397
2023		0
Thereafter		0
Accrued Expenses
Commitment and Contingencies
Foreign exchange hedges assets			83
Other liabilities
Commitment and Contingencies
Foreign exchange hedges assets			$ 28
Equipment and Construction Contracts
Commitment and Contingencies
Purchase commitment	€ 1.4	1,333
St. Clair Location \| Equipment and Construction Contracts
Commitment and Contingencies
Purchase commitment	0.4	422
Arkansas Location \| Equipment and Construction Contracts
Commitment and Contingencies
Purchase commitment	€ 1.0	$ 1,157