Significant Accounting Policies (Details) (USD $)	3 Months Ended														1 Months Ended		7 Months Ended	1 Months Ended			7 Months Ended	3 Months Ended		1 Months Ended						12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014 Alnylam [Member]	Mar. 31, 2014 Collaborations and Licensing Agreements [Member] Agreement Item	Mar. 31, 2014 Collaborations and Licensing Agreements [Member] Development milestones - new development candidate [Member] Minimum [Member]	Mar. 31, 2014 Collaborations and Licensing Agreements [Member] Development milestones - new development candidate [Member] Maximum [Member]	Mar. 31, 2014 Collaborations and Licensing Agreements [Member] Development milestones - Phase 1 [Member] Minimum [Member]	Mar. 31, 2014 Collaborations and Licensing Agreements [Member] Development milestones - Phase 1 [Member] Maximum [Member]	Mar. 31, 2014 Collaborations and Licensing Agreements [Member] Development milestones - Phase 2 [Member] Minimum [Member]	Mar. 31, 2014 Collaborations and Licensing Agreements [Member] Development milestones - Phase 2 [Member] Maximum [Member]	Mar. 31, 2014 Collaborations and Licensing Agreements [Member] Development milestones - Phase 3 [Member] Minimum [Member]	Mar. 31, 2014 Collaborations and Licensing Agreements [Member] Development milestones - Phase 3 [Member] Maximum [Member]	Mar. 31, 2014 Collaborations and Licensing Agreements [Member] Regulatory milestones [Member] Minimum [Member]	Mar. 31, 2014 Collaborations and Licensing Agreements [Member] Regulatory milestones [Member] Maximum [Member]	Jun. 30, 2013 AstraZeneca [Member] Agreement entered into in December 2012 [Member]	Dec. 31, 2012 AstraZeneca [Member] Agreement entered into in December 2012 [Member] Target Item Drug	Jun. 30, 2013 AstraZeneca [Member] Agreement entered into in December 2012 [Member]	Dec. 31, 2012 AstraZeneca [Member] Agreement entered into in December 2012 [Member] ISIS-AR [Member] Item	Jun. 30, 2013 AstraZeneca [Member] Agreement entered into in December 2012 [Member] ISIS-STAT3 License [Member]	Dec. 31, 2012 AstraZeneca [Member] Agreement entered into in December 2012 [Member] ISIS-STAT3 License [Member]	Jun. 30, 2013 AstraZeneca [Member] Agreement entered into in December 2012 [Member] ISIS-STAT3 License [Member]	Mar. 31, 2014 Biogen Idec [Member] Collaborations and Licensing Agreements [Member] Collaboration	Mar. 31, 2014 Biogen Idec [Member] Collaborations and Licensing Agreements [Member] Agreement	Jan. 31, 2012 Biogen Idec [Member] Agreement entered into in January 2012 [Member]	Jun. 30, 2012 Biogen Idec [Member] Agreement entered into in June 2012 [Member]	Dec. 31, 2012 Biogen Idec [Member] Agreement entered into in December 2012 [Member] Target	Sep. 30, 2013 Biogen Idec [Member] Agreement entered into in September 2013 [Member]	May 31, 2011 GSK [Member] Collaborations and Licensing Agreements [Member]	Mar. 31, 2010 GSK [Member] Collaborations and Licensing Agreements [Member]	Dec. 31, 2013 GSK [Member] Collaborations and Licensing Agreements [Member] Convertible notes guarantee obligation [Member] Drug
Research and development revenue under collaborative agreements
Number of targets																5										3
Upfront fee received															$ 6,000,000	$ 25,000,000	$ 31,000,000							$ 29,000,000	$ 12,000,000	$ 30,000,000	$ 100,000,000	$ 3,000,000	$ 35,000,000
Number of drugs collaborative partner may license under the separate research program																3
Number of units of accounting																4		1
Upfront fee recognized																			2,200,000	9,300,000
Upfront fee deferred																	19,500,000										100,000,000
Assumed change in estimated selling price (in hundredths)																					10.00%
Percentage by which earned revenue would change based on assumed change in estimated selling price (in hundredths)																					7.00%
Amount by which earned revenue would change based on assumed change in estimated selling price																					750,000
Number of collaborative agreements																						4	4
Number of new development candidates added to collaboration																														2
Decrease in amortization of upfront payments for 2014				2,600,000
Term of agreement																						6 years	6 years
Number of categories of milestone events				3
Number of stages of life-cycle of drugs				3
Completion period					12 months	18 months	1 year	2 years	1 year	3 years	2 years	4 years
Time to prepare and submit regulatory filings													6 months	12 months
Time to obtain approval													1 year	2 years
Example of sales threshold as milestone event				1,000,000,000
Licensing and royalty revenue	$ 8,611,000	$ 1,689,000	$ 7,700,000