Outstanding Shares of Potentially Dilutive Securities Excluded from Calculation of Dilutive Net Loss per Share (Detail)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding shares of potentially dilutive securities	23,122,737	10,808,969	9,686,543
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding shares of potentially dilutive securities	9,957,367	9,521,970	8,410,765
Common stock subject to repurchase
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding shares of potentially dilutive securities	2,942	34,832	99,110
Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding shares of potentially dilutive securities	1,871,907	252,167	176,668
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding shares of potentially dilutive securities	1,385,000	1,000,000	1,000,000
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	9,905,521