Income Taxes - Deferred Tax (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Net operating losses and tax credits	$ 46,336	$ 43,990
Stock-based compensation expense	3,883	3,579
Deferred rent	1,483	1,148
Depreciation and amortization expense	61	631
Accrued expenses	192	234
Allowance for doubtful accounts	1	19
Other	95	157
Total deferred tax assets before valuation allowance	52,051	49,758
Less: valuation allowance	(50,211)	(45,932)
Total deferred tax assets, net of valuation allowance	1,840	3,826
Deferred tax liabilities:
Intangible assets	(2,277)	(4,324)
Other	(10)	(12)
Total deferred tax liabilities	(2,287)	(4,336)
Total deferred tax liabilities, net	(447)	$ (510)
Increase in net valuation allowance	$ 4,279