Commitments and Contingencies - Additional Information (Detail) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012 sqft	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012 sqft	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Tekmira Restructured Cross-License Agreement	Dec. 31, 2012 Tekmira Restructured Cross-License Manufacturing Contracts and Service Agreement	Dec. 31, 2012 Tekmira Restructured Cross-License Buy-Down	Dec. 31, 2012 Bmr Fresh Pond Research Park Llc sqft	Dec. 31, 2008 Third Street Lease
Loss Contingencies [Line Items]
Future purchase commitments	$ 11,100,000								$ 11,100,000
Future purchase commitments expected to be incurred in 2013	10,300,000								10,300,000
Future purchase commitments expected to be incurred past 2013	800,000								800,000
Area of office and laboratory space held under operating lease	129,000								129,000						15,000
Lease expiration date									2016-09
Number 0f lease extension options									2						2
Lease extension period									5 years						5 years
Area of premises subleased									34,014
Lease expiration date									Sep. 30, 2016						Aug. 31, 2017
Expected future sublease receivable	10,000,000								10,000,000
Lease incentive received															1,800,000	7,300,000
Rent expense									6,400,000	6,500,000	6,400,000
Operating expenses	96,844,000	34,906,000	32,951,000	31,480,000	34,041,000	33,229,000	33,732,000	36,573,000	196,181,000	137,575,000	144,111,000	65,000,000
One time settlement payment	65,000,000								65,000,000				30,000,000	35,000,000
Contingent milestone payments														10,000,000
Future milestone payments												$ 5,000,000