Revenue from United States and European Union Governments Contracts and Other Revenue (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Revenue [Line Items]
U.S. and E.U. governments contract revenue	$ 2,583	$ 2,951	$ 8,671	$ 7,425
July 2010 Contract (Ebola and Marburg IV) [Member]
Revenue [Line Items]
U.S. and E.U. governments contract revenue	1,709	2,076	5,773	4,690
August 2012 Agreement (Intramuscular) [Member]
Revenue [Line Items]
U.S. and E.U. governments contract revenue		439		2,245
November 2012 SKIP-NMD Agreement (DMD) [Member]
Revenue [Line Items]
U.S. and E.U. governments contract revenue	24	9	1,389	63
Children's National Medical Center [Member]
Revenue [Line Items]
U.S. and E.U. governments contract revenue	0	0	659	0
Carolinas Medical Center Agreement [Member]
Revenue [Line Items]
U.S. and E.U. governments contract revenue	850		850
Other Agreements [Member]
Revenue [Line Items]
U.S. and E.U. governments contract revenue		$ 427		$ 427