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	9 Months Ended
	Sep. 30, 2018	Sep. 30, 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	2,989	4,072
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	1,378	2,489
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	1,611	1,566