Summary of Significant Accounting Policies - Schedule of Calculation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
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)	4,384	5,231	2,504
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)	3,865	3,171	529
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)	237	85	0
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)	282	1,975	1,975