Restructuring Charges (Details) - Employee Separation Costs - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Costs incurred and charged to expense	$ 1,873	$ 2,526	$ 1,489
Restructuring Reserve [Roll Forward]
Accrued liability beginning balance	244	209	1,404
Costs incurred and charged to expense	1,873	2,526	1,489
Cash payments	(1,362)	(2,491)	(2,684)
Accrued liability ending balance	$ 755	$ 244	$ 209