Commitments and Contingencies - Additional Information (Detail) (USD $)	1 Months Ended			12 Months Ended					12 Months Ended
	Nov. 30, 2013 sqft	Apr. 30, 2013	Feb. 28, 2013 CreditFacility	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Lease Agreements [Member]	Jun. 30, 2013 Lease Agreements [Member]	Dec. 31, 2013 Corvallis, Oregon
Commitments and Contingencies [Line Items]
Letters of credit amount issued			$ 7,300,000					$ 600,000
Lease agreement, expiration period							7 years
Lease agreement, average base rent due current				3,535,000			2,400,000
Lease agreement, average base rent year two				3,807,000			2,400,000
Lease agreement, average base rent year three				3,895,000			2,400,000
Lease agreement, average base rent year four				3,986,000			2,400,000
Lease agreement, average base rent year five				4,079,000			2,400,000
Lease agreement, average base rent year six							2,400,000
Lease agreement, average base rent year seven							2,400,000
Additional rental space under amendment	15,077
Total rental space	61,453
Additional base rate	500,000
Percentage of annual increase in lease	2.50%								3.00%
Monthly rent									79,000
Rent expense under leases				3,400,000	2,600,000	2,500,000
Notice period to terminate license agreements				6 months
Royalty payments				100,000	100,000	100,000
Maximum royalty to Charley's Fund				3,400,000
Upfront and development milestone payments		7,100,000
Upfront payments recognized under agreement				1,100,000
Lawsuit filling date				January 2014
Law affected under lawsuit filling				The complaints allege that the defendants violated the federal securities laws in connection with disclosures related to eteplirsen
Lawsuit claim amount				4,000,000
Certificate of deposit purchased			7,300,000
Certificate of deposit maturity date				2014-04
Restricted investments				$ 7,250,000
Number of letter of credit			2