Net Loss Per Share - Outstanding Options, Warrants and Preferred Stock Excluded from Computation of Diluted Net Loss per Share (Detail) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding options, warrants and preferred stock excluded from computation of diluted net loss per share	2,113	1,686	686
Convertible Preferred Stock (as Converted) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding options, warrants and preferred stock excluded from computation of diluted net loss per share		8,631	7,567
Convertible Preferred Stock Warrants (as Converted) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding options, warrants and preferred stock excluded from computation of diluted net loss per share		607	509
Common Stock Warrant [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding options, warrants and preferred stock excluded from computation of diluted net loss per share	618		1