Common Stock and Preferred Stock - Carrying Value of Warrants to Purchase Shares of Preferred Stock (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Equity [Abstract]
Beginning balance	$ 3,532	$ 2,497	$ 42
Issuance of preferred stock warrants	138	648	2,528
Warrant revaluation	(1,156)	387	(73)
Reclassification to common stock warrants	(2,514)
Ending balance		$ 3,532	$ 2,497