Net Loss per Share - Outstanding Options, Warrants and Preferred Stock Excluded from Computation of Diluted Net Loss per Share (Detail)	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Convertible preferred stock (as converted)
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	2,127,463	2,126,982
Options to purchase common stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	593,663	595,577
Warrant | Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	931	931
Warrant | Convertible preferred stock (as converted)
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	136,908	50,681