U.S. Government Agreement and Collaboration - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended		6 Months Ended		1 Months Ended			6 Months Ended	17 Months Ended	1 Months Ended
	Feb. 28, 2011	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Feb. 28, 2011 Minimum	Feb. 28, 2011 Maximum	Feb. 28, 2011 Contract from HHS BARDA	Jun. 30, 2012 Contract from HHS BARDA	Jun. 30, 2012 Contract from HHS BARDA	Feb. 28, 2011 Additional contract with HHS BARDA option
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract amount	$ 179,000,000							$ 97,000,000			$ 82,000,000
Contractual base-period								36 months			24 months
Contract revenue		7,103,000	3,001,000	11,745,000	3,835,000				11,400,000	26,100,000
Expected clinical trial costs recoded as cost of contract revenue	3,100,000
Clinical trial costs recoded as cost of contract revenue				$ 2,400,000
Agreement termination year	2027
Percentage of reimbursements of certain development and product costs and royalty payments						10.00%	20.00%