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Cumulative amount of payments received under the collaboration agreement as of the end of the reporting period.

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The maximum amount of development milestone payments to be received over the term of the collaboration.

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The maximum amount of development milestone payments to be received for each medicine that achieves marketing approval over the term of the collaboration.

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The maximum amount of license fees to be received over the term of the collaboration.

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The maximum amount of license fees to be received for each medicine that achieves marketing approval over the term of the collaboration.

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The maximum amount of payments the Company is eligible to receive over the term of the collaboration.

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The maximum amount of payments the Company is eligible to receive for each medicine that achieves marketing approval over the term of the collaboration.

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The maximum amount of regulatory milestone payments to be received over the term of the collaboration.

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The maximum amount of regulatory milestone payments to be received for each medicine that achieves marketing approval over the term of the collaboration.

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The maximum amount of sales milestone payments to be received over the term of the collaboration.

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Maximum royalty payments under the royalty purchase agreement made before royalty interest reverts back to the Company.

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The next payment to be achieved under the collaboration agreement.

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The percentage of royalty payments paid on annual sales of medicine.

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The cash premium paid on the purchase of the Company's common stock under the collaboration agreement.

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The amount of consideration the Company earned or is eligible to earn under the collaboration agreement, including any variable consideration.

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Royalty percentage received on the net sales of a medicine by a collaboration partner under the collaboration agreement.

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The amount of upfront payments received during the period under the collaboration agreement.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable.

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Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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Collaborative Arrangements and Licensing Agreements, Biogen (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Jun. 30, 2024 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2017 USD ($)	Jan. 31, 2023 USD ($)	Apr. 30, 2018 USD ($)	Dec. 31, 2012 PerformanceObligation
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue			$ 705,138	$ 787,647	$ 587,367
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
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%
Maximum royalty payments made before royalty interest reverts back			$ 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%
Maximum royalty payments made before royalty interest reverts back			$ 550,000					$ 550,000
SPINRAZA Royalties [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue			216,090	240,379	242,314
Biogen [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue			368,058	350,146	$ 366,696
Deferred contract revenue			$ 211,000	$ 307,400
Biogen [Member] \| Revenue [Member] \| Strategic Partner [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Concentration percentage			52.00%	44.00%	62.00%
SPINRAZA [Member] \| Minimum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments received			$ 2,200,000
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]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments received			$ 1,800,000
SPINRAZA [Member] \| SPINRAZA R&D Revenue [Member] \| Minimum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments received			425,000
2013 Neurology [Member] \| Minimum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments received			$ 110,000
2013 Neurology [Member] \| QALSODY [Member] \| Minimum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Royalty percentage received on net sales of medicine			11.00%
2013 Neurology [Member] \| QALSODY [Member] \| Maximum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Royalty percentage received on net sales of medicine			15.00%
2013 Neurology [Member] \| QALSODY Royalties [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments received			$ 3,000
2013 Neurology [Member] \| QALSODY R&D Revenue [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments received			108,000
New Antisense Medicines for the Treatment of SMA [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments received			$ 85,000
Royalty percentage received on net sales of medicine			20.00%
Upfront payment received							$ 25,000
Next payment to be achieved			$ 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
Maximum amount of development milestone payments over term of collaboration			45,000
Maximum amount of regulatory milestone payments over term of collaboration			110,000
Maximum amount of sales milestone payments over term of collaboration			400,000
Revenue						$ 60,000
2018 Neurology [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments received			$ 1,100,000
Royalty percentage received on net sales of medicine			20.00%
Upfront payment received		$ 375,000
Next payment to be achieved			$ 15,000
Transaction price									$ 552,000
Premium paid on shares purchased		$ 177,000
Cumulative payments included in transaction price for performance obligation			623,000
Maximum amount of payments receivable per medicine over term of collaboration			270,000
Maximum amount of license fees per medicine over term of collaboration			15,000
Maximum amount of development milestone payments per medicine over term of collaboration			105,000
Maximum amount of regulatory milestone payments per medicine over term of collaboration			150,000
2012 Neurology [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Maximum amount of payments receivable over term of collaboration			185,000
Maximum amount of license fees over term of collaboration			45,000
Maximum amount of development milestone payments over term of collaboration			10,000
Maximum amount of regulatory milestone payments over term of collaboration			130,000
Next payment to be achieved			25,000
Number of separate performance obligations \| PerformanceObligation										2
Revenue	$ 30
2012 Neurology [Member] \| Minimum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments received			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
2012 Neurology [Member] \| ION582 [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments included in transaction price for performance obligation			$ 68,000