Restructuring - Narrative (Details)	3 Months Ended			6 Months Ended
	Jun. 30, 2017 USD ($) employee	Mar. 31, 2017 USD ($) employee	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, number of positions eliminated | employee	17	20
Restructuring	$ 1,060,000		$ 0	$ 1,734,000	$ 0
Restructuring and related cost, obligations to be satisfied, term				12 months
Restructuring and related Cost, estimate of sublease payments to be received				$ 1,300,000
Lease obligations	2,300,000			2,300,000
Additional restructuring charges expected	100,000			100,000
Cash and cash equivalents	13,487,000		$ 25,441,000	13,487,000	$ 25,441,000	$ 16,629,000	$ 34,640,000
Debt obligations	0			0
Impact of restructuring activities on operating expenses, excluding restructuring and asset impairment charges	(2,900,000)			(3,600,000)
Restructuring Initiative 2017
Restructuring Cost and Reserve [Line Items]
Restructuring initiative, reduction of annual operating costs, amount	8,000,000	$ 10,000,000
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