Restructuring - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Restructuring	$ 1,000	$ (200,000)	$ (46,000)	$ 1,534,000
Restructuring and related cost, obligations to be satisfied, term			12 months
Cash and cash equivalents	7,054,000	$ 11,935,000	$ 7,054,000	11,935,000	$ 10,761,000	$ 16,629,000
Debt obligations	$ 0		0
Impact of restructuring activities on operating expenses, excluding restructuring and asset impairment charges			$ 3,100,000
Severance and Related Benefits
Restructuring Cost and Reserve [Line Items]
Restructuring				700,000
Facilities
Restructuring Cost and Reserve [Line Items]
Restructuring				600,000
Other
Restructuring Cost and Reserve [Line Items]
Restructuring				$ 200,000