Collaborative Arrangements and Licensing Agreements, Biogen (Details) $ in Thousands	1 Months Ended		3 Months Ended						12 Months Ended
	Sep. 30, 2013 USD ($) PerformanceObligation	Dec. 31, 2012 USD ($) Program	Dec. 31, 2022 USD ($) Medicine	Sep. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($) PerformanceObligation	Dec. 31, 2022 USD ($) Medicine	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2018 USD ($)	Jan. 31, 2023 USD ($)	Apr. 30, 2018 USD ($) PerformanceObligation
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue									$ 587,367	$ 810,456	$ 729,264
SPINRAZA [Member] | Subsequent Event [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of annual sales on which royalty payments are paid													$ 1,500,000
SPINRAZA [Member] | Minimum [Member] | Subsequent Event [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Percentage of royalty payments paid to Royalty Pharma on annual sales of medicine													25.00%
Maximum royalty payments made before royalty interest reverts back													$ 475,000
SPINRAZA [Member] | Maximum [Member] | Subsequent Event [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Percentage of royalty payments paid to Royalty Pharma on annual sales of medicine													45.00%
Maximum royalty payments made before royalty interest reverts back													$ 550,000
SPINRAZA Royalties [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue									242,314	267,776	286,583
R&D Revenue [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue									284,009	468,061	364,565
Biogen [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue									366,700	428,800	$ 408,600
Deferred revenue			$ 351,200		$ 407,500				$ 351,200	$ 407,500
Biogen [Member] | Revenue [Member] | Strategic Partner [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Concentration percentage									62.00%	53.00%	56.00%
Biogen [Member] | Minimum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments received			3,400,000						$ 3,400,000
Biogen [Member] | SPINRAZA Royalties [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue									242,300	$ 267,800	$ 286,600
Biogen [Member] | R&D Revenue [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue									124,400	161,000	122,000
SPINRAZA [Member] | Minimum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative revenue earned			1,800,000						$ 1,800,000
Royalty percentage received on net sales of medicine									11.00%
SPINRAZA [Member] | Maximum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Royalty percentage received on net sales of medicine									15.00%
SPINRAZA [Member] | SPINRAZA Royalties [Member] | Minimum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative revenue earned			1,400,000						$ 1,400,000
SPINRAZA [Member] | R&D Revenue [Member] | Minimum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative revenue earned			425,000						425,000
New Antisense Medicines for the Treatment of SMA [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments received			85,000						$ 85,000
Royalty percentage received on net sales of medicine									20.00%
Upfront payment received								$ 25,000
Maximum amount of payments receivable over term of collaboration			1,200,000						$ 1,200,000
Maximum amount of upfront payments over term of collaboration			25,000						25,000
Maximum amount of license fees over term of collaboration			110,000						110,000
Maximum amount of development milestone payments over term of collaboration			80,000						80,000
Maximum amount of regulatory milestone payments over term of collaboration			180,000						180,000
Maximum amount of sales milestone payments over term of collaboration			800,000						800,000
Next payment to be achieved			45,000						45,000
Number of separate performance obligations | PerformanceObligation								1
Transaction price								$ 25,000
New Antisense Medicines for the Treatment of SMA [Member] | ION306 [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payments receivable over term of collaboration			555,000						555,000
Maximum amount of development milestone payments over term of collaboration			45,000						45,000
Maximum amount of regulatory milestone payments over term of collaboration			110,000						110,000
Maximum amount of sales milestone payments over term of collaboration			400,000						400,000
Revenue					$ 60,000
2018 Strategic Neurology [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments received			1,100,000						$ 1,100,000
Royalty percentage received on net sales of medicine									20.00%
Upfront payment received							$ 375,000
Next payment to be achieved			7,500						$ 7,500
Number of separate performance obligations | PerformanceObligation														1
Transaction price														$ 552,000
Term of collaboration agreement									10 years
Upfront payment received, including purchase of stock							1,000,000
Proceeds from issuance of common stock							$ 625,000
Percentage cash premium paid on shares purchased							25.00%
Maximum amount of payments receivable per medicine over term of collaboration			270,000						$ 270,000
Maximum amount of license fees per medicine over term of collaboration			15,000						15,000
Maximum amount of development milestone payments per medicine over term of collaboration			105,000						105,000
Maximum amount of regulatory milestone payments per medicine over term of collaboration			150,000						150,000
Premium paid on shares purchased							$ 177,000
Cumulative payments included in transaction price for performance obligation			616,000						616,000
Milestone payments achieved and included in transaction price for performance obligation										$ 23,000	11,000
2013 Strategic Neurology [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments received			300,000						300,000
Upfront payment received	$ 100,000
Next payment to be achieved			$ 16,000						$ 16,000
Number of separate performance obligations | PerformanceObligation	1
Transaction price	$ 100,000
Number of medicines currently being advanced | Medicine			5						5
Maximum amount of payments receivable per antisense molecule over term of collaboration			$ 260,000						$ 260,000
Maximum amount of license fees per antisense molecule over term of collaboration			70,000						70,000
Maximum amount of development milestone payments per antisense molecule over term of collaboration			60,000						60,000
Maximum amount of regulatory milestone payments per antisense molecule over term of collaboration			$ 130,000						$ 130,000
Revenue				$ 9,000								$ 35,000
2013 Strategic Neurology [Member] | R&D Revenue [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments included in transaction price for performance obligation											145,000
2013 Strategic Neurology [Member] | Medicines for Parkinson's Disease [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Number of medicines currently being advanced | Medicine			1						1
2013 Strategic Neurology [Member] | Medicines for ALS [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Number of medicines currently being advanced | Medicine			2						2
2013 Strategic Neurology [Member] | Medicines for Multiple System Atrophy [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Number of medicines currently being advanced | Medicine			1						1
2013 Strategic Neurology [Member] | Medicines for Undisclosed Targets [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Number of medicines currently being advanced | Medicine			1						1
2013 Strategic Neurology [Member] | Tofersen [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payments receivable over term of collaboration			$ 110,000						$ 110,000
Maximum amount of license fees over term of collaboration			35,000						35,000
Maximum amount of development milestone payments over term of collaboration			18,000						18,000
Maximum amount of regulatory milestone payments over term of collaboration			55,000						55,000
2012 Neurology [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments received			170,000						170,000
Upfront payment received		$ 30,000
Maximum amount of payments receivable over term of collaboration			210,000						210,000
Maximum amount of license fees over term of collaboration			70,000						70,000
Maximum amount of development milestone payments over term of collaboration			10,000						10,000
Maximum amount of regulatory milestone payments over term of collaboration			130,000						130,000
Next payment to be achieved			25,000						25,000
Number of programs under which medicines are to be developed and commercialized | Program		2
2012 Neurology [Member] | R&D Revenue [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments included in transaction price for performance obligation			40,000						40,000
2012 Neurology [Member] | IONIS-MAPT [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments included in transaction price for performance obligation			57,000						57,000
Milestone payments achieved and included in transaction price for performance obligation											$ 19,500
Revenue						$ 45,000			10,000
2012 Neurology [Member] | ION582 [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Milestone payments achieved and included in transaction price for performance obligation			$ 14,500
Revenue									$ 20,000