Arcion License Agreement - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Common stock locking period			9 months
Milestone payments increased			$ 8,000,000
Research and development expense	12,758,215	6,546,579	24,790,383	11,258,189
US [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Potential Payments upon achieving certain pre-determined sales thresholds in the U.S			60,000,000
US [Member] | Minimum [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone Sales			200,000,000
Milestone payment receivable from sublicensees			70,000,000
Arcion License Agreement [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Share issued to Arcion			500,516
Fair market value of unregistered shares issued			2,100,000
Potential payments upon filing and acceptance			2,500,000
Royalty term description			The royalty term for any given country is the later of (i) the first date there are no valid claims against any Arcion patent, (ii) expiration of patent exclusivity or (iii) tenth anniversary of the first commercial sale.
Research and development expense			2,100,000
Arcion License Agreement [Member] | Minimum [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Potential milestone payment upon FDA approval			17,500,000
Arcion License Agreement [Member] | Maximum [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Potential milestone payment upon FDA approval			$ 35,000,000