Potentially Dilutive Securities Excluded From Computation of Diluted Net Loss Per Share Attributable to Common Stockholders (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities, excluded from computation of diluted net income (loss) per share	5,356,647	1,458,936	5,356,647	3,914,108
Employee Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities, excluded from computation of diluted net income (loss) per share	3,979,813	1,454,417	3,979,813	2,725,525
Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities, excluded from computation of diluted net income (loss) per share	1,135,929	37	1,135,929	914,587
Employee Stock Purchase Plan
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities, excluded from computation of diluted net income (loss) per share	236,423		236,423	269,514
Common Stock Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities, excluded from computation of diluted net income (loss) per share	4,482	4,482	4,482	4,482