Collaborative Arrangements and Licensing Agreements (Details) (USD $)	3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended		1 Months Ended			6 Months Ended	7 Months Ended	6 Months Ended				7 Months Ended			1 Months Ended	3 Months Ended				6 Months Ended		3 Months Ended		6 Months Ended			1 Months Ended	6 Months Ended	7 Months Ended					1 Months Ended	6 Months Ended				1 Months Ended	6 Months Ended				1 Months Ended	6 Months Ended	1 Months Ended							6 Months Ended	1 Months Ended		3 Months Ended		6 Months Ended		1 Months Ended	6 Months Ended				1 Months Ended	6 Months Ended		6 Months Ended		1 Months Ended		6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended			1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended				3 Months Ended	1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 Maximum [Member]	Jun. 30, 2014 AstraZeneca [Member] Collaborations and Licensing Agreements [Member]	Jun. 30, 2013 AstraZeneca [Member] Collaborations and Licensing Agreements [Member]	Jun. 30, 2014 AstraZeneca [Member] Collaborations and Licensing Agreements [Member]	Jun. 30, 2013 AstraZeneca [Member] Collaborations and Licensing Agreements [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	Dec. 31, 2012 AstraZeneca [Member] Agreement entered into in December 2012 [Member] Drug	Jun. 30, 2014 AstraZeneca [Member] Agreement entered into in December 2012 [Member]	Jun. 30, 2013 AstraZeneca [Member] Agreement entered into in December 2012 [Member]	Jun. 30, 2014 AstraZeneca [Member] Agreement entered into in December 2012 [Member] Forecast [Member]	Jun. 30, 2014 AstraZeneca [Member] Agreement entered into in December 2012 [Member] Pre-specified events [Member]	Jun. 30, 2014 AstraZeneca [Member] Agreement entered into in December 2012 [Member] Regulatory milestones [Member]	Jun. 30, 2014 AstraZeneca [Member] Agreement entered into in December 2012 [Member] Research and development milestones [Member]	Jun. 30, 2013 AstraZeneca [Member] Agreement entered into in December 2012 [Member] ISIS-AR [Member]	Jun. 30, 2013 AstraZeneca [Member] Agreement entered into in December 2012 [Member] Three drugs [Member] Drug	Jun. 30, 2013 AstraZeneca [Member] Agreement entered into in December 2012 [Member] ISIS-STAT3 License [Member]	Aug. 31, 2013 AstraZeneca [Member] Agreement entered into in August 2013 [Member]	Jun. 30, 2014 AstraZeneca [Member] Agreement entered into in August 2013 [Member]	Jun. 30, 2014 AstraZeneca [Member] Agreement entered into in August 2013 [Member] Regulatory milestones [Member]	Jun. 30, 2014 AstraZeneca [Member] Agreement entered into in August 2013 [Member] License fee and substantive milestones [Member]	Jun. 30, 2014 AstraZeneca [Member] Agreement entered into in August 2013 [Member] Research and development milestones [Member]	Jun. 30, 2014 Biogen Idec [Member] ISIS-SMN [Member]	Jun. 30, 2014 Biogen Idec [Member] ISIS-SMN [Member] Open label extension [Member]	Jun. 30, 2014 Biogen Idec [Member] Collaborations and Licensing Agreements [Member]	Jun. 30, 2013 Biogen Idec [Member] Collaborations and Licensing Agreements [Member]	Jun. 30, 2014 Biogen Idec [Member] Collaborations and Licensing Agreements [Member] Collaboration	Jun. 30, 2014 Biogen Idec [Member] Collaborations and Licensing Agreements [Member] Agreement	Jun. 30, 2013 Biogen Idec [Member] Collaborations and Licensing Agreements [Member]	Jan. 31, 2012 Biogen Idec [Member] Agreement entered into in January 2012 [Member] ISIS-SMN [Member]	Jun. 30, 2014 Biogen Idec [Member] Agreement entered into in January 2012 [Member] ISIS-SMN [Member]	Jul. 31, 2014 Biogen Idec [Member] Agreement entered into in January 2012 [Member] ISIS-SMN [Member]	Mar. 31, 2014 Biogen Idec [Member] Agreement entered into in January 2012 [Member] ISIS-SMN [Member]	Jun. 30, 2014 Biogen Idec [Member] Agreement entered into in January 2012 [Member] ISIS-SMN [Member] Regulatory milestones [Member]	Jun. 30, 2014 Biogen Idec [Member] Agreement entered into in January 2012 [Member] ISIS-SMN [Member] License fee and substantive milestones [Member]	Jun. 30, 2014 Biogen Idec [Member] Agreement entered into in January 2012 [Member] ISIS-SMN [Member] Research and development milestones [Member]	Jun. 30, 2012 Biogen Idec [Member] Agreement entered into in June 2012 [Member] ISIS-DMPK [Member]	Jun. 30, 2014 Biogen Idec [Member] Agreement entered into in June 2012 [Member] ISIS-DMPK [Member]	Jun. 30, 2014 Biogen Idec [Member] Agreement entered into in June 2012 [Member] ISIS-DMPK [Member] Regulatory milestones [Member]	Jun. 30, 2014 Biogen Idec [Member] Agreement entered into in June 2012 [Member] ISIS-DMPK [Member] License fee and substantive milestones [Member]	Jun. 30, 2014 Biogen Idec [Member] Agreement entered into in June 2012 [Member] ISIS-DMPK [Member] Research and development milestones [Member]	Dec. 31, 2012 Biogen Idec [Member] Agreement entered into in December 2012 [Member] Neurology [Member] Target	Jun. 30, 2014 Biogen Idec [Member] Agreement entered into in December 2012 [Member] Neurology [Member]	Jun. 30, 2014 Biogen Idec [Member] Agreement entered into in December 2012 [Member] Neurology [Member] Regulatory milestones [Member]	Jun. 30, 2014 Biogen Idec [Member] Agreement entered into in December 2012 [Member] Neurology [Member] License fee and substantive milestones [Member]	Jun. 30, 2014 Biogen Idec [Member] Agreement entered into in December 2012 [Member] Neurology [Member] Research and development milestones [Member]	Sep. 30, 2013 Biogen Idec [Member] Agreement entered into in September 2013 [Member] Strategic Neurology [Member]	Jun. 30, 2014 Biogen Idec [Member] Agreement entered into in September 2013 [Member] Strategic Neurology [Member]	Sep. 30, 2013 Biogen Idec [Member] Agreement entered into in September 2013 [Member] Strategic Neurology [Member] Maximum [Member]	Jun. 30, 2014 Biogen Idec [Member] Agreement entered into in September 2013 [Member] Strategic Neurology [Member] Antisense drug for neurological disease [Member] Regulatory milestones [Member]	Jun. 30, 2014 Biogen Idec [Member] Agreement entered into in September 2013 [Member] Strategic Neurology [Member] Antisense drug for neurological disease [Member] License fee and substantive milestones [Member]	Jun. 30, 2014 Biogen Idec [Member] Agreement entered into in September 2013 [Member] Strategic Neurology [Member] Antisense drug for neurological disease [Member] Research and development milestones [Member]	Jun. 30, 2014 Biogen Idec [Member] Agreement entered into in September 2013 [Member] Strategic Neurology [Member] Other modalities [Member] Pre-specified events [Member]	Jun. 30, 2014 Biogen Idec [Member] Agreement entered into in September 2013 [Member] Strategic Neurology [Member] Other modalities [Member] Regulatory milestones [Member]	Jun. 30, 2014 Biogen Idec [Member] Agreement entered into in September 2013 [Member] Strategic Neurology [Member] Other modalities [Member] Research and development milestones [Member]	Jun. 30, 2014 Biogen Idec [Member] Period of Performance through June, 2014 [Member] ISIS-SMN [Member] Phase 2 [Member]	May 31, 2011 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member]	Mar. 31, 2010 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member]	Jun. 30, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member]	Jun. 30, 2013 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member]	Jun. 30, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] Program	Jun. 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	Jun. 30, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] Pre-specified events [Member]	Jun. 30, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] Regulatory milestones [Member]	Jun. 30, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] Commercialization milestones [Member]	Jun. 30, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] Research and development milestones [Member]	Dec. 31, 2012 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] ISIS-TTR [Member]	Jun. 30, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] ISIS-TTR [Member]	Jun. 30, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] ISIS-TTR [Member] Research and development milestones [Member]	Jun. 30, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] Isis-HBV [Member] Development milestones [Member]	Jun. 30, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] Isis-HBV [Member] Research and development milestones [Member]	Apr. 30, 2014 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] Isis GSK4 [Member]	Nov. 30, 2013 Glaxo Smith Kline [Member] Collaborations and Licensing Agreements [Member] Isis GSK4 [Member] Research and development milestones [Member]	Jun. 30, 2014 Achaogen Inc [Member] Collaborations and Licensing Agreements [Member] Drug	Dec. 31, 2006 Achaogen Inc [Member] Collaborations and Licensing Agreements [Member] Series A preferred stock [Member]	Jun. 30, 2014 Achaogen Inc [Member] Collaborations and Licensing Agreements [Member] Maximum [Member]	Dec. 31, 2013 Achaogen Inc [Member] Collaborations and Licensing Agreements [Member] Maximum [Member]	Dec. 31, 2009 Achaogen Inc [Member] Collaborations and Licensing Agreements [Member] Pre-specified events [Member]	Jun. 30, 2014 Achaogen Inc [Member] Collaborations and Licensing Agreements [Member] Pre-specified events [Member]	Mar. 31, 2004 Alnylam [Member] Collaborations and Licensing Agreements [Member]	Jun. 30, 2014 Alnylam [Member] Collaborations and Licensing Agreements [Member]	Jun. 30, 2013 Alnylam [Member] Collaborations and Licensing Agreements [Member]	Jun. 30, 2014 Alnylam [Member] Collaborations and Licensing Agreements [Member]	Jun. 30, 2013 Alnylam [Member] Collaborations and Licensing Agreements [Member]	Dec. 31, 2013 Alnylam [Member] Collaborations and Licensing Agreements [Member] Phase 3 [Member]	Jun. 30, 2014 Alnylam [Member] Collaborations and Licensing Agreements [Member] Pre-specified events [Member]	Jun. 30, 2014 Alnylam [Member] Collaborations and Licensing Agreements [Member] Regulatory milestones [Member]	Jun. 30, 2014 Alnylam [Member] Collaborations and Licensing Agreements [Member] Research and development milestones [Member]	Jun. 30, 2014 Alnylam's collaboration with Genzyme [Member] Collaborations and Licensing Agreements [Member]	Apr. 30, 2013 Roche [Member] Collaborations and Licensing Agreements [Member]	Jun. 30, 2014 Roche [Member] Collaborations and Licensing Agreements [Member]	Jun. 30, 2013 Roche [Member] Collaborations and Licensing Agreements [Member]	Jun. 30, 2014 Roche [Member] Collaborations and Licensing Agreements [Member]	Jun. 30, 2013 Roche [Member] Collaborations and Licensing Agreements [Member]	Jun. 30, 2014 Roche [Member] Collaborations and Licensing Agreements [Member] HTT [Member] Regulatory milestones [Member]	Jun. 30, 2014 Roche [Member] Collaborations and Licensing Agreements [Member] HTT [Member] Commercialization milestones [Member]	Jun. 30, 2014 Roche [Member] Collaborations and Licensing Agreements [Member] HTT [Member] Research and development milestones [Member]	Jun. 30, 2014 Roche [Member] Collaborations and Licensing Agreements [Member] Each Additional Drug [Member] Development, regulatory and commercial milestones [Member]	Jun. 30, 2014 Roche [Member] Collaborations and Licensing Agreements [Member] Brain Shuttle [Member] Commercialization milestones [Member]	Jun. 30, 2014 Roche [Member] Agreement entered into in April 2013 [Member] Maximum [Member]
Collaborative Arrangements and Licensing Agreements
Number of targets											5	5																																		3
Number of drugs the collaborative partner may license under a separate research program											3	3								3
Upfront and near-term payments											$ 31,000,000	$ 31,000,000
Upfront fee received										6,000,000		25,000,000		31,000,000								750,000												29,000,000												30,000,000					100,000,000											35,000,000										2,500,000													5,000,000										30,000,000
Upfront fee recorded as deferred revenue														19,500,000					11,200,000	7,600,000	700,000																				12,000,000										100,000,000														7,900,000												142,000,000
Number of collaborations																															4	4
Period of exclusive rights to use antisense technology																																																			6 years
Period during which a change in control could result in requirement to refund upfront payment																																																			6 years		6 years
Milestone payment earned													15,000,000		19,500,000																											14,000,000																			3,000,000												1,000,000			3,000,000		5,000,000												750,000
Cumulative milestone payments earned under collaborative arrangement at period end													25,000,000																															24,000,000											10,000,000																			26,000,000									3,000,000
Payment received related to the amendment of clinical development plan																											9,300,000	5,500,000																																3,800,000
Number of programs under which drugs are to be developed																																																																	5		6
Increase in payments that the Company is eligible to receive under collaboration																																			35,000,000
Maximum amount of payment receivable																955,000,000	655,000,000	300,500,000						105,000,000	163,200,000	45,300,000												150,000,000	303,800,000	78,800,000			130,000,000	259,000,000	35,000,000			130,000,000	259,000,000	59,000,000																		1,200,000,000	483,500,000	428,000,000	172,000,000			43,000,000										46,300,000																170,000,000	80,000,000	67,000,000		50,000,000	362,000,000
Maximum amount of payment receivable per drug																																																						130,000,000		60,000,000	90,000,000	55,000,000	57,000,000
Cumulative milestone payments received under collaborative arrangement at period end																																				17,300,000
Next prospective milestone													15,000,000										3,300,000				18,000,000															35,000,000					10,000,000					10,000,000																1,500,000											4,000,000									375,000							22,000,000
Maximum milestone payments through Phase 2 proof of concept for each program, except TTR and the 5th target																																																														20,000,000			1,500,000
Maximum amount of payments receivable per drug under strategic alliance																																																							260,000,000																																				3,400,000	2,300,000	1,100,000
Maximum amount of payments receivable per program																																																																																																							136,500,000
Revenue earned	57,076,000	38,092,000	85,237,000	81,451,000		15,640,000	15,300,000	19,100,000	17,800,000	11,500,000																			34,500,000	7,400,000		44,700,000	11,200,000																														3,500,000	2,300,000	6,800,000	12,200,000									10,000,000	1,000,000										0	0	7,700,000	300,000					7,700,000		2,400,000	1,300,000	4,400,000	1,300,000
Percent of total revenue (in hundredths)						27.00%		22.00%																					60.00%		52.00%	52.00%																															6.00%		8.00%
Potential payable on drug development																																																																																											3,400,000
Deferred revenue						5,500,000		5,500,000																					136,300,000		136,300,000	136,300,000					9,300,000																										9,100,000		9,100,000																															21,000,000		21,000,000
Upfront fee in the form of equity securities																																																																																1,500,000
Number of drugs to be developed and commercialized																																																																															2
Ownership interest percentage (in hundredths)					20.00%																																																																												10.00%	10.00%
Number of shares held after conversion (in shares)																																																																															148,000
Fair value of investment in Achaogen, Inc																																																																															1,900,000
Cumulative revenue recognized to date																																																																																						48,200,000		48,200,000
Payment received in form of securities																																																																																			$ 500,000