Summary of Significant Accounting Policies - Schedule of Calculation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares outstanding excluded from calculation of diluted net income per share (shares)	4,092	4,384	5,231
Shares subject to outstanding common stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares outstanding excluded from calculation of diluted net income per share (shares)	3,770	3,865	3,171
Shares subject to outstanding restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares outstanding excluded from calculation of diluted net income per share (shares)	289	237	85
Shares subject to outstanding warrants to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares outstanding excluded from calculation of diluted net income per share (shares)	33	282	1,975