Segment Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2025 USD ($) Segment	Mar. 31, 2024 USD ($)
Segment Information [Abstract]
Number of operating segments | Segment	1
Revenue	$ 131,612	$ 119,497
Cost of sales	1,463	2,151
Selling, general and administrative	76,250	52,644
Net loss	(146,938)	(142,803)
Ionis Operations [Member]
Segment Information [Abstract]
Revenue	131,612	119,497
Cost of sales	1,363	1,952
Drug discovery	26,989	28,171
Drug development	112,946	125,751
Medical affairs	5,642	4,676
Manufacturing and development chemistry	14,281	11,441
R&D support	20,553	21,946
Selling, general and administrative	66,980	43,733
Other segment items	29,796	24,630
Net loss	$ (146,938)	$ (142,803)
Segment Reporting, Other Segment Item, Composition, Description	Other segment items include stock-based compensation expense, investment income, interest expense, gain or loss on investments, other income or expense and income tax expense or benefit.