United States Government Contracts - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended
	Oct. 31, 2010 2010 Qualifying Therapeutic Discovery Project	Dec. 31, 2012 July 2010 Agreement (Ebola and Marburg) Segment	Dec. 31, 2012 Phase one Marburg	Dec. 31, 2012 Phase two three four Marburg	Aug. 29, 2012 August 2012 Agreement (Intramuscular administration)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of segments		4
Period of performance spanning		4 years
Funding outstanding			$ 15,900,000
Estimated funding				84,400,000
Funding to evaluate the feasibility of intramuscular route of administration					3,900,000
Number of cash grants	5
Grant revenue recognized	$ 1,200,000