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Cumulative payments received since inception of the collaboration agreement included in the transaction price for the performance obligation.

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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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Milestone payment achieved during the period.

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No definition available.

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The next potential payment to be earned under the collaboration agreement.

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No definition available.

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The number of medicines currently being developed under the collaboration agreement(s).

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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			9 Months Ended
	Sep. 30, 2020 USD ($) Medicine	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) Medicine	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue	$ 160,079		$ 167,892	$ 438,983	$ 628,918
SPINRAZA Royalties [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue	74,171		81,672	211,925	211,884
R&D Revenue [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue	$ 64,739		72,193	$ 169,948	376,833
Biogen [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Number of medicines currently being developed \| Medicine	8			8
Revenue	$ 125,400		$ 107,200	$ 310,500	$ 293,800
Deferred revenue	$ 475,500			$ 475,500		$ 525,800
Biogen [Member] \| Revenue [Member] \| Strategic Partner [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Concentration percentage	78.00%		64.00%	71.00%	47.00%
Biogen [Member] \| Minimum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Cumulative payments received	$ 2,700,000			$ 2,700,000
Biogen [Member] \| SPINRAZA Royalties [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue	74,200		$ 81,700	211,900	$ 211,900
Biogen [Member] \| R&D Revenue [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue	51,200		25,500	98,600	$ 81,900
2012 Neurology [Member] \| Maximum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Next prospective payment	25,000			25,000
2012 Neurology [Member] \| IONIS-MAPT [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Milestone payment achieved	12,000	$ 7,500
Cumulative payments included in transaction price for performance obligation	57,000			57,000
2013 Strategic Neurology [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue	18,000		$ (16,500)
2013 Strategic Neurology [Member] \| Maximum [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Next prospective payment	10,000			$ 10,000
2013 Strategic Neurology [Member] \| ION464 [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue	18,000
2013 Strategic Neurology [Member] \| ION541 [Member]
Collaborative Arrangement and Licensing Agreement [Abstract]
Revenue	$ 10,000