Commitments and Contingencies - Additional Information (Detail) (USD $)	1 Months Ended			3 Months Ended			3 Months Ended	1 Months Ended	3 Months Ended
	Nov. 30, 2013 sqft	Apr. 30, 2013	Feb. 28, 2013 CreditFacility	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Mar. 31, 2014 Assignors [Member]	Jan. 31, 2014 Sublease [Member] sqft	Mar. 31, 2014 Sublease [Member]	Mar. 31, 2014 Corvallis, Oregon [Member]	Mar. 31, 2014 Lease Agreements [Member]	Jun. 30, 2013 Lease Agreements [Member]
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				3,807,000							2,400,000
Lease agreement, average annual base rent year two				3,895,000							2,400,000
Lease agreement, average annual base rent year three				3,986,000							2,400,000
Lease agreement, average annual base rent year four				4,079,000							2,400,000
Lease agreement, average base rent year five											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							15,077
Total rental space	61,453
Additional annual base rent	500,000
Percentage of annual increase in lease	2.50%									3.00%
Lease agreement period								18 months	18 months
Total subleases base rent								700,000
Annual base rent										900,000
Rent expense under leases				1,100,000	600,000
Notice period to terminate license agreements				6 months
Royalty payments				100,000	100,000
Maximum royalty to Charley's Fund				3,400,000
Upfront and development milestone payments				0	0
Obligated to make milestone payments				23,400,000
Receivables under satisfaction of milestones				21,100,000
Upfront payments recognized under agreement		7,100,000					300,000
Development and commercial milestone payments							2,700,000
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						2014-05
Restricted investments				$ 7,250,000		$ 7,250,000
Number of letter of credit			2