Basic and Diluted Net Loss Per Share - Outstanding Shares of Potentially Dilutive Securities Excluded from Calculation of Diluted Net Loss per Share (Detail) - shares	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding shares of potentially dilutive securities	31,819,339	33,432,413
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding shares of potentially dilutive securities	10,252,607	11,363,128
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding shares of potentially dilutive securities	1,525,736	2,028,289
Warrants to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding shares of potentially dilutive securities	1,250,000	1,250,000
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	18,790,996	18,790,996