Restructuring - Narrative (Details) - USD ($)	3 Months Ended		15 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Restructuring	$ (50,000)	$ 674,000
Restructuring and related cost, obligations to be satisfied, term	12 months
Cash and cash equivalents	$ 10,172,000	14,970,000	$ 10,172,000	$ 10,761,000	$ 16,629,000
Debt obligations	0		0
Impact of restructuring activities on operating expenses, excluding restructuring and asset impairment charges	$ (1,900,000)
Severance and Related Benefits
Restructuring Cost and Reserve [Line Items]
Restructuring		643,000
Facilities
Restructuring Cost and Reserve [Line Items]
Restructuring		19,000
Other
Restructuring Cost and Reserve [Line Items]
Restructuring		$ 11,000
Maximum
Restructuring Cost and Reserve [Line Items]
Impact of restructuring activities on operating expenses, excluding restructuring and asset impairment charges			$ (10,700,000)