Organization and Significant Accounting Policies, Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	2 Months Ended	3 Months Ended				10 Months Ended	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2022		Dec. 31, 2021		Oct. 31, 2020	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Apr. 30, 2021	Dec. 31, 2019
Basic Net Income (Loss) per Share [Abstract]
Basic net loss per share (in dollars per share)		$ (0.37)	[1],[2]	$ 1.59	[1],[2]		$ (1.9)	$ (0.2)	$ (3.18)
Net loss							$ (269,722)	$ (28,597)	$ (444,263)
Income (loss) available to Ionis common stockholders				$ 224,612					$ (444,464)
Weighted average shares outstanding (in shares)				141,205			141,848	141,021	139,612
0.125% Notes [Member]
Basic Net Income (Loss) per Share [Abstract]
Interest rate on convertible senior notes	0.125%	0.125%		0.125%			0.125%	0.125%	0.125%		0.125%
1% Notes [Member]
Basic Net Income (Loss) per Share [Abstract]
Interest rate on convertible senior notes	1.00%	1.00%		1.00%			1.00%	1.00%	1.00%	1.00%	1.00%
0% Notes [Member]
Basic Net Income (Loss) per Share [Abstract]
Interest rate on convertible senior notes		0.00%		0.00%			0.00%	0.00%		0.00%	0.00%
Ionis [Member]
Basic Net Income (Loss) per Share [Abstract]
Net loss									$ (246,702)
Akcea [Member]
Basic Net Income (Loss) per Share [Abstract]
Percentage ownership		100.00%					100.00%
Akcea [Member]
Basic Net Income (Loss) per Share [Abstract]
Weighted average shares owned in Akcea (in shares)						77,095
Basic net loss per share (in dollars per share)						$ (1.45)
Net loss	$ (85,987)					$ (111,775)			$ (197,762)

[1] We compute net income (loss) per share independently for each quarter during the year.

[2] As discussed in Note 1, Organization and Significant Accounting Policies, we compute basic net income (loss) per share by dividing the total net income (loss) by our weighted-average number of common shares outstanding during the period.