Restructuring Charges (Details) - Employee Separation Costs - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Restructuring Cost and Reserve [Line Items]
Costs incurred and charged to expense	$ 1,320	$ 2,271
Restructuring Reserve [Roll Forward]
Accrued liability beginning balance	244
Costs incurred and charged to expense	1,320
Cash payments	(976)
Accrued liability ending balance	$ 588