Net Loss Per Share - Outstanding Options, Warrants and Preferred Stock Excluded from Computation of Basic and Diluted Net Loss Per Share (Detail) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 Stock options [Member]	Mar. 31, 2013 Stock options (as converted) [Member]	Mar. 31, 2013 Convertible preferred stock (as converted) [Member]	Mar. 31, 2013 Convertible preferred stock warrants (as converted) [Member]	Mar. 31, 2014 Common stock warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share	3,169	1,806	8,631	607	618