Outstanding Shares of Potentially Dilutive Securities Excluded from Calculation of Diluted Net Loss per Share (Detail)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding shares of potentially dilutive securities	24,202,653	28,257,450
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding shares of potentially dilutive securities	11,142,893	10,637,489
Common stock subject to repurchase
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding shares of potentially dilutive securities	584	24,151
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding shares of potentially dilutive securities	2,218,578	955,310
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding shares of potentially dilutive securities	1,250,000	1,500,000
Shares of common stock to be issued upon conversion of the Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding shares of potentially dilutive securities	9,590,598	15,140,500