Collaborative Arrangements and Licensing Agreements, GlaxoSmithKline (Details) (USD $)	3 Months Ended		9 Months Ended		1 Months Ended		3 Months Ended		9 Months Ended		1 Months Ended					1 Months Ended		1 Months Ended		1 Months Ended			1 Months Ended	9 Months Ended	0 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	May 31, 2011 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member]	Mar. 31, 2010 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member]	Sep. 30, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member]	Sep. 30, 2013 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member]	Sep. 30, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] Program	Sep. 30, 2013 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member]	Mar. 31, 2010 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] Maximum [Member] Program	Sep. 30, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] Pre-specified events [Member]	Sep. 30, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] Development milestones [Member]	Sep. 30, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] Regulatory milestones [Member]	Sep. 30, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] Commercialization milestones [Member]	Dec. 31, 2012 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] ISIS-TTR [Member]	Sep. 30, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] ISIS-TTR [Member]	Oct. 31, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] ISIS-TTR [Member] Subsequent Event [Member]	Sep. 30, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] ISIS-TTR [Member] Research and development milestones [Member] Phase 2/3 Study [Member]	Jun. 30, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] ISIS-HBV [Member]	Sep. 30, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] ISIS-HBV [Member]	Sep. 30, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] ISIS-HBV [Member] Pre-specified events [Member]	Sep. 30, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] ISIS-GSK4 [Member]	Sep. 30, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] ISIS-GSK4 [Member]	Nov. 07, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] ISIS-GSK5 [Member] Subsequent Event [Member]	Nov. 07, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] ISIS-GSK4 and ISIS-GSK5 [Member]	Sep. 30, 2014 Glaxo Smith Kline [Member] Collaboration and Licensing Agreement - Upfront Fees and Other Payments [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Number of programs under which drugs are to be developed									5		6
Upfront fee received						$ 35,000,000										$ 2,500,000				$ 1,000,000
Milestone payment earned					3,000,000													18,000,000					1,500,000	6,500,000	5,000,000
Maximum milestone payments through Phase 2 proof of concept for each program, except TTR and the 5th target						20,000,000
Cumulative milestone payments earned under collaborative arrangement at period end																	27,000,000				10,000,000					11,500,000
Maximum amount of payment receivable												1,200,000,000	147,500,000	483,500,000	428,000,000				25,000,000
Next prospective milestone																						1,000,000
Revenue earned	44,063,000	23,585,000	129,300,000	105,036,000			5,100,000	11,300,000	11,900,000	23,500,000
Percent of total revenue (in hundredths)							12.00%		9.00%
Deferred revenue							$ 11,100,000		$ 11,100,000																		$ 9,000,000