Revenue - Additional Information (Detail) (USD $)	6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended	67 Months Ended	1 Months Ended	3 Months Ended		6 Months Ended			3 Months Ended	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 Small Business Innovative Research	Jun. 30, 2011 Small Business Innovative Research	Jun. 30, 2012 Small Business Innovative Research	Jun. 30, 2011 Small Business Innovative Research	Jun. 30, 2011 Stanley Medical Research Institute	Jun. 30, 2011 Stanley Medical Research Institute	Jun. 30, 2012 Stanley Medical Research Institute	Oct. 31, 2010 Vulcan Incorporated	Jun. 30, 2012 Vulcan Incorporated	Jun. 30, 2011 Vulcan Incorporated	Jun. 30, 2012 Vulcan Incorporated	Jun. 30, 2011 Vulcan Incorporated	Oct. 21, 2010 Vulcan Incorporated	Jun. 30, 2011 Life Sciences Discovery Fund Authority	Jun. 30, 2012 Life Sciences Discovery Fund Authority	Jun. 30, 2011 Life Sciences Discovery Fund Authority	Oct. 21, 2010 Life Sciences Discovery Fund Authority
Revenue [Line Items]
Grant revenue recognized			$ 329,000	$ 121,000	$ 489,000	$ 209,000	$ 94,000	$ 227,000								$ 553,000	$ 624,000	$ 1,000,000
Remaining available amount under grant			1,400,000		1,400,000
Grants received									5,700,000	20,000,000
Cost reduction to intellectual property assets										10,800,000
Fair value of warrants issued										994,000
Deferred revenue											3,700,000		3,700,000		8,200,000
Maximum contractual amount from grant																			5,000,000
Reductions to deferred revenue											1,300,000	401,000	2,000,000	958,000
Revenue recognized											1,200,000	387,000	1,900,000	934,000
Cost reduction to assets	$ 59,000	$ 1,636,000									$ 60,000	$ 14,000	$ 60,000	$ 24,000		$ 1,600,000		$ 1,600,000