Restructuring Costs - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 1,228	$ 153
Scenario, Forecast
Restructuring Cost and Reserve [Line Items]
Severance Costs			$ 3,000
Accrued Liabilities
Restructuring Cost and Reserve [Line Items]
Restructuring reserve	356
Accounts Payable
Restructuring Cost and Reserve [Line Items]
Restructuring reserve	288
2019 Corporate Restructuring Obligations
Restructuring Cost and Reserve [Line Items]
Restructuring costs	1,398
Restructuring reserve	644			$ 0
Lyon France Workforce Reduction
Restructuring Cost and Reserve [Line Items]
Restructuring costs	170
Restructuring reserve	$ 63	$ 824		$ 879	$ 1,000
Employee Severance | Corporate Workforce Reduction
Restructuring Cost and Reserve [Line Items]
Expected number of positions eliminated (as a percent)						50.00%
Employee Severance | Lyon France Workforce Reduction
Restructuring Cost and Reserve [Line Items]
Expected number of positions eliminated (as a percent)						50.00%