Severance and Other Charges - Severance, Exit and Other Charges (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Total severances and other charges	$ (480)	$ 2,555
Employee severance expense
Restructuring Cost and Reserve [Line Items]
Total severances and other charges	139	1,227
Lease exit costs
Restructuring Cost and Reserve [Line Items]
Total severances and other charges	$ (619)	$ 1,328