Net Loss Per Share - Summary of Shares Excluded from Calculation of Diluted Loss Per Share with a Potential Dilutive Impact (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded from calculation of diluted loss per share with a potential dilutive impact	3,567	4,198
Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded from calculation of diluted loss per share with a potential dilutive impact	1,683	2,987
Common Stock Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded from calculation of diluted loss per share with a potential dilutive impact		17
Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded from calculation of diluted loss per share with a potential dilutive impact	1,884	1,194