Net Loss Per Share - Potentially Dilutive Securities Not Included in Calculation of Diluted Net Loss per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities not included in calculation of diluted net loss per share (in shares)	1,674,119	4,027,897	5,050,929
Convertible note payable
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities not included in calculation of diluted net loss per share (in shares)	0	1,461,474	1,411,659
Common stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities not included in calculation of diluted net loss per share (in shares)	1,674,119	2,566,423	3,639,270