Net Loss per Share of Common Stock - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share, Basic and Diluted
Net loss attributable to common stockholders	$ (21,013)	$ (21,761)	$ (8,819)
Weighted-average number of shares used in computing net loss per share of common stock, basic and diluted	48,158,378	46,718,495	44,958,120
Net loss per share of common stock, basic and diluted (in dollars per share)	$ (0.44)	$ (0.47)	$ (0.20)
Stock options to purchase common stock
Antidilutive potential common shares excluded from computation of diluted net loss per share
Antidilutive potential common shares	11,312,218	10,480,891	6,468,743
Redeemable Convertible Preferred Stock
Antidilutive potential common shares excluded from computation of diluted net loss per share
Antidilutive potential common shares	258,878	897,231	850,351
Warrant
Antidilutive potential common shares excluded from computation of diluted net loss per share
Antidilutive potential common shares		90,000	912,368

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Antidilution
-URI http://asc.fasb.org/extlink&oid=6505113

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Diluted Earnings Per Share
-URI http://asc.fasb.org/extlink&oid=6510752

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Contingent Stock Agreement
-URI http://asc.fasb.org/extlink&oid=6508534

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=7655603&loc=d3e1377-109256

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