Collaborative Arrangements and Licensing Agreements, AstraZeneca (Details) $ in Thousands	1 Months Ended		3 Months Ended							12 Months Ended
	Jul. 31, 2015 USD ($) PerformanceObligation	Dec. 31, 2012 USD ($)	Dec. 31, 2020 USD ($) Agreement Medicine	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) Program	Sep. 30, 2018 USD ($)	Mar. 31, 2018 USD ($) LicenseFee	Dec. 31, 2020 USD ($) Agreement Medicine	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue										$ 729,264	$ 1,122,599	$ 599,674
R&D Revenue [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue										$ 364,565	770,149	$ 344,752
AstraZeneca [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Number of collaboration agreements | Agreement			2							2
Deferred revenue			$ 10,000			$ 25,000				$ 10,000	$ 25,000
AstraZeneca [Member] | Revenue [Member] | Strategic Partner [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Concentration percentage										12.00%	3.00%	20.00%
AstraZeneca [Member] | Minimum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments received			$ 380,000							$ 380,000
AstraZeneca [Member] | R&D Revenue [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue										$ 88,000	$ 28,100	$ 120,700
Cardiovascular, Renal and Metabolic Diseases [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Number of collaboration agreements | Agreement			1							1
Number of licensed medicines | Medicine			4							4
Upfront payment received	$ 65,000
Minimum amount of payments receivable for license fees and milestones			$ 5,500,000							$ 5,500,000
Maximum amount of payments receivable for development milestones			1,100,000							1,100,000
Maximum amount of payments receivable for regulatory milestones			2,900,000							2,900,000
Maximum amount of payments receivable for commercialization milestones			1,500,000							1,500,000
Next prospective payment			30,000							30,000
Number of separate performance obligations | PerformanceObligation	1
Transaction price	$ 65,000
Number of license fees earned | LicenseFee									2
Revenue			20,000
Cardiovascular, Renal and Metabolic Diseases [Member] | Minimum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments received			235,000							235,000
Cardiovascular, Renal and Metabolic Diseases [Member] | ION455 [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue			30,000							30,000
Cardiovascular, Renal and Metabolic Diseases [Member] | ION532 and ION449 [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue										30,000
Cardiovascular, Renal and Metabolic Diseases [Member] | ION532 [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue					$ 10,000				$ 30,000
Cardiovascular, Renal and Metabolic Diseases [Member] | ION839 [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue						$ 10,000			$ 30,000
Cardiovascular, Renal and Metabolic Diseases [Member] | ION449[Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue			20,000					$ 10,000
Cardiovascular, Renal and Metabolic Diseases [Member] | R&D Revenue [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments included in transaction price for performance obligation			$ 90,000							$ 90,000
Oncology [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Number of collaboration agreements | Agreement			1							1
Upfront payment received		$ 31,000
Minimum amount of payments receivable for license fees and milestones			$ 265,000							$ 265,000
Maximum amount of payments receivable for development milestones			107,000							107,000
Maximum amount of payments receivable for regulatory milestones			105,000							105,000
Next prospective payment			12,000							12,000
Number of programs advanced | Program							2
Oncology [Member] | Minimum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments received			$ 140,000							140,000
Oncology [Member] | Danvatirsen [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue							$ 17,500
Oncology [Member] | ION736 [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue				$ 13,000			$ 10,000			$ 13,000