Net Loss Per Share - Antidilutive Securities (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share amount	5,525	4,670	5,244	4,356
Shares subject to outstanding stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share amount	4,942	4,227	4,696	3,973
Shares subject to outstanding restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share amount	555	415	520	355
Shares subject to outstanding warrants to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share amount	28	28	28	28