Strategic Alliances and Collaborations - Additional Information (Detail) (USD $)	3 Months Ended		1 Months Ended	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Oct. 31, 2012 Astra Zeneca	Mar. 31, 2013 Astra Zeneca Agreement	Mar. 31, 2013 Astra Zeneca Preclinical	Mar. 31, 2013 Astra Zeneca Clinical	Mar. 31, 2013 Astra Zeneca Commercialization	Mar. 31, 2013 Astra Zeneca Minimum	Mar. 31, 2013 Astra Zeneca Maximum	Mar. 31, 2013 GSK	Mar. 31, 2013 GSK Immuno-Inflammatory Alliance	Mar. 31, 2013 GSK Immuno-Inflammatory Alliance Preclinical	Mar. 31, 2013 GSK Immuno-Inflammatory Alliance Clinical	Mar. 31, 2013 GSK Immuno-Inflammatory Alliance Commercialization	Mar. 31, 2013 GSK Immuno-Inflammatory Alliance Regulatory	Mar. 31, 2013 GSK Immuno-Inflammatory Alliance Fourth Micro RNA Targets	Mar. 31, 2013 GSK Immuno-Inflammatory Alliance Development Candidate	Mar. 31, 2013 GSK Immuno-Inflammatory Alliance Phase One Clinical Trial	Mar. 31, 2013 GSK Immuno-Inflammatory Alliance Phase Two Clinical Trial	Mar. 31, 2013 GSK Immuno-Inflammatory Alliance Proof-of-Concept Trial	Mar. 31, 2013 GSK Immuno-Inflammatory Alliance Minimum	Mar. 31, 2013 GSK Immuno-Inflammatory Alliance Maximum	Mar. 31, 2013 GSK HCV Alliance	Mar. 31, 2013 GSK HCV Alliance Preclinical	Mar. 31, 2013 GSK HCV Alliance Clinical	Mar. 31, 2013 GSK HCV Alliance Regulatory	Mar. 31, 2013 GSK HCV Alliance Phase One Clinical Trial	Mar. 31, 2013 GSK HCV Alliance Phase Two Clinical Trial	Mar. 31, 2013 GSK HCV Alliance Proof-of-Concept Trial	Mar. 31, 2013 GSK HCV Alliance Commercialization Milestones	Mar. 31, 2013 GSK HCV Alliance Minimum	Mar. 31, 2013 GSK HCV Alliance Maximum	Mar. 31, 2013 Sanofi	Mar. 31, 2013 Sanofi Three Remaining Micro RNA Targets	Mar. 31, 2013 Sanofi Each of Four Micro RNA Targets	Mar. 31, 2013 Biogen Idec	Mar. 31, 2013 Biogen Idec Research Tax Credit Carryforward	Mar. 31, 2013 Biogen Idec Identification Of Micro Rna Biomarker	Mar. 31, 2013 Biogen Idec Validation Of Micro Rna Biomarker	Mar. 31, 2013 Biogen Idec Longitudinal Study Of Patient Samples On Ms Therapy
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue recognition period										8 years
Deferred revenue										$ 5.6
Revenue through milestone payments				498,000,000	5,000,000	123,000,000	370,000,000				432,500,000	15,500,000	87,000,000	180,000,000	150,000,000	500,000	5,000,000	4,000,000	5,000,000	20,000,000			144,500,000	5,500,000	29,000,000	50,000,000	4,000,000	5,000,000	20,000,000	60,000,000				5,000,000	15,000,000		1,300,000	250,000	500,000	500,000
Royalties based on percentage of net sales								10.00%	20.00%												10.00%	20.00%									10.00%	20.00%
Upfront payment being recognized as revenue																																	25,000,000			800,000
Revenue recognition period																																	5 years			2 years
Number of collaborative areas granted				3
Collaboration and license agreement date				August 2012																																August 2012
Received upfront payment				3,000,000																																800,000
Expected term of research and development plan			4 years
Common stock issue	36,000	36,000		25,000,000
Common stock issued	35,965,371	35,831,808		6,250,000
Price per share	$ 0.001	$ 0.001		$ 4.00
Number of days during which AstraZeneca could not sell, transfer, make any short sale of, or grant any option for the sale of any common stock				365 days
Restricting common stock valuation measurement period				1 year
Restricting common stock valuation, discounted amount				4.3
Issued promissory note	$ 5,000,000
Conversion to common stock	1,256,232
Conversion rate	$ 4.00