Collaborative Arrangements and Licensing Agreements, Biogen (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2023 USD ($) Medicine	Jun. 30, 2018 USD ($)	Dec. 31, 2023 USD ($) Medicine	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($) PerformanceObligation Program	Jan. 31, 2023 USD ($)	Apr. 30, 2018 USD ($) PerformanceObligation	Sep. 30, 2013 USD ($) PerformanceObligation
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue			$ 787,647	$ 587,367	$ 810,456
SPINRAZA Royalties [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue			240,379	242,314	267,776
R&D Revenue [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue			479,056	284,009	468,061
SPINRAZA [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of annual sales on which royalty payments are paid	$ 1,500,000		$ 1,500,000							$ 1,500,000
SPINRAZA [Member] | Minimum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Percentage of royalty payments paid to Royalty Pharma on annual sales of medicine	25.00%		25.00%							25.00%
Maximum royalty payments made before royalty interest reverts back	$ 475,000		$ 475,000							$ 475,000
SPINRAZA [Member] | Maximum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Percentage of royalty payments paid to Royalty Pharma on annual sales of medicine	45.00%		45.00%							45.00%
Maximum royalty payments made before royalty interest reverts back	$ 550,000		$ 550,000							$ 550,000
Biogen [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue			350,146	366,696	$ 428,784
Deferred revenue	307,400		$ 307,400	$ 351,200
Biogen [Member] | Revenue [Member] | Strategic Partner [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Concentration percentage			44.00%	62.00%	53.00%
Biogen [Member] | Maximum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments received	3,800,000		$ 3,800,000
SPINRAZA [Member] | Minimum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative revenue earned	2,100,000		$ 2,100,000
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	1,600,000		$ 1,600,000
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
Next payment to be achieved	45,000		$ 45,000
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
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
Next payment to be achieved	15,000		15,000
Premium paid on shares purchased		$ 177,000
Cumulative payments included in transaction price for performance obligation	623,000		623,000
Milestone payments achieved and included in transaction price for performance obligation	7,500
2013 Strategic Neurology [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments received	325,000		325,000
Upfront payment received								$ 100,000
Number of separate performance obligations | PerformanceObligation												1
Transaction price												$ 100,000
Next payment to be achieved	$ 70,000		$ 70,000
Cumulative payments included in transaction price for performance obligation						$ 145,000
Number of medicines currently being advanced | Medicine	4		4
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			$ 16,000
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] | QALSODY [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
Next payment to be achieved	20,000		$ 20,000
2013 Strategic Neurology [Member] | QALSODY [Member] | Minimum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Royalty percentage received on net sales of medicine			11.00%
2013 Strategic Neurology [Member] | QALSODY [Member] | Maximum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Royalty percentage received on net sales of medicine			15.00%
2012 Neurology [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
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
Number of separate performance obligations | PerformanceObligation									2
Next payment to be achieved	70,000		70,000
Number of programs under which medicines are to be developed and commercialized | Program									2
2012 Neurology [Member] | Minimum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments received	230,000		230,000
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				$ 10,000
2012 Neurology [Member] | ION582 [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments included in transaction price for performance obligation	$ 68,000		68,000
Milestone payments achieved and included in transaction price for performance obligation			$ 39,000