Restructuring Charges - Roll-Forward of Accrued Restructuring Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Restructuring Reserve [Roll Forward]
Accrued at January 1, 2018	$ 23
Restructuring charges	571	$ 0
Payments	(78)
Accrued at March 31, 2018	516
Severance expenses [Member]
Restructuring Reserve [Roll Forward]
Accrued at January 1, 2018	0
Restructuring charges	366
Payments	(70)
Accrued at March 31, 2018	296
Write-downs and retirements of fixed assets [Member]
Restructuring Reserve [Roll Forward]
Accrued at January 1, 2018	0
Restructuring charges	48
Payments	0
Accrued at March 31, 2018	48
Lease cancellations [Member]
Restructuring Reserve [Roll Forward]
Accrued at January 1, 2018	23
Restructuring charges	157
Payments	(8)
Accrued at March 31, 2018	$ 172