Common Stock Warrants - Additional Informational (Detail) (USD $)	1 Months Ended			1 Months Ended		1 Months Ended
	Jul. 27, 2012	Jul. 31, 2012	Sep. 30, 2012	Jun. 30, 2011 Oxford/SVB	Dec. 31, 2011 Oxford/SVB	Jul. 31, 2011 Cowen Royalty	Sep. 30, 2012 Cowen Royalty	Dec. 31, 2011 Cowen Royalty
Schedule Of Common Stock [Line Items]
Shares of common stock exercisable through warrants		15,776,235		26,455		225,000
Warrants exercise price per share	$ 2.50	$ 2.50		$ 3.78		$ 9.00
Fair value of warrant liabilities			$ 24,505,000		$ 76,000		$ 410,000	$ 345,000
Term of common stock warrant exercisable (years)		5 years		7 years		10 years
Warrants exercisable date	Jul. 27, 2013	Jul. 27, 2013
Warrants expiry date	July 27, 2017	July 27, 2017