Common Stock Warrants - Additional Informational (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	0 Months Ended		1 Months Ended					1 Months Ended
	Jul. 27, 2012	Jul. 18, 2011	Jul. 18, 2011	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Healthcare Royalty	Dec. 31, 2012 Healthcare Royalty	Jun. 30, 2011 Oxford/SVB [Member]	Dec. 31, 2011 Oxford/SVB [Member]
Schedule Of Common Stock [Line Items]
Shares of common stock exercisable through warrants	15,784,200							26,455
Warrants exercisable date	Jul. 27, 2013
Warrants exercise price per share	$ 2.50							$ 3.78
Warrants expiry date	July 27, 2017
Term of common stock warrant exercisable (years)	5 years	10 years						7 years
Fair value of warrant liabilities				$ 13,490	$ 9,308	$ 261	$ 185
Warrant exercisable to Healthcare Royalty, shares		225,000	225,000
Warrant exercisable to Healthcare Royalty, price per share (usd per share)		$ 9.00
Unamortized debt discount									$ 76