Revenue from United States Government Contracts and Other Revenue (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenue [Line Items]
U.S. government contract revenue	$ 27	$ 1,059	$ 2,583	$ 6,088	$ 2,626	$ 4,168	$ 2,951	$ 4,474	$ 9,757	$ 14,219	$ 37,329
July 2010 Agreement (Ebola and Marburg Intravenous Administration) [Member]
Revenue [Line Items]
U.S. government contract revenue									6,816	9,064	36,557
June 2010 Agreement (H1N1/Influenza) [Member]
Revenue [Line Items]
U.S. government contract revenue										427
August 2012 Agreement (Intramuscular administration) [Member]
Revenue [Line Items]
U.S. government contract revenue										2,791	673
European Union SKIP-NMD Agreement (DMD) [Member]
Revenue [Line Items]
U.S. government contract revenue									1,432	1,263
Children's National Medical Center Agreement (DMD) [Member]
Revenue [Line Items]
U.S. government contract revenue									659	674
Carolinas Medical Center Agreement (DMD) [Member]
Revenue [Line Items]
U.S. government contract revenue									850
Other Agreements [Member]
Revenue [Line Items]
U.S. government contract revenue											$ 99