Restructuring - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Restructuring	$ 3,000	$ 1,060,000	$ (47,000)	$ 1,734,000
Restructuring and related cost, obligations to be satisfied, term			12 months
Cash and cash equivalents	8,619,000	13,487,000	$ 8,619,000	13,487,000	$ 10,761,000	$ 16,629,000
Debt obligations	$ 0		0
Impact of restructuring activities on operating expenses, excluding restructuring and asset impairment charges			$ 3,400,000
Severance and Related Benefits
Restructuring Cost and Reserve [Line Items]
Restructuring		127,000		700,000
Facilities
Restructuring Cost and Reserve [Line Items]
Restructuring		900,000		900,000
Other
Restructuring Cost and Reserve [Line Items]
Restructuring		$ 107,000		$ 119,000