Common Stock Equivalent Shares Excluded from Computation of Diluted Net Loss per Share (Detail) - shares	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Stock options to purchase common stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	5,615,484	4,787,869
Common stock warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	1,500	1,500
Restricted Stock Units (RSUs)
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	318,228	171,787
Performance Shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	293,694	140,000