Fourth Quarter Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2022		Dec. 31, 2021		Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Apr. 30, 2021	Dec. 31, 2019
Fourth Quarter Financial Data (Unaudited) [Abstract]
Revenue	$ 151,890	[1]	$ 440,006
Operating expenses	359,909	[2]	219,403		$ 997,558	$ 840,642	$ 901,346
Loss from operations	(208,019)		220,603		(410,191)	(30,186)	(172,082)
Net income (loss)	$ (52,430)	[3]	$ 224,613		$ (269,722)	$ (28,597)	$ (479,743)
Basic net income (loss) per share (in dollars per share)	$ (0.37)	[4],[5]	$ 1.59	[4],[5]	$ (1.9)	$ (0.2)	$ (3.18)
Diluted net income (loss) per share (in dollars per share)	$ (0.37)	[4]	$ 1.41	[4],[6]	$ (1.9)	$ (0.2)	$ (3.18)
Gain on sale of real estate assets	$ 150,100				$ 150,135	$ 0	$ 0
Income (Numerator) [Abstract]
Income (loss) available to Ionis common stockholders			$ 224,612				$ (444,464)
Net income available to Ionis common shareholders			$ 226,210
Shares (Denominator) [Abstract]
Shares used in computing basic net loss per share (in shares)			141,205		141,848	141,021	139,612
Effect of Diluted Securities [Abstract]
Shares issuable related to our ESPP (in shares)			34
Shares used in computing diluted net income per share (in shares)			160,340		141,848	141,021	139,612
0 Percent Convertible Senior Notes [Member]
Fourth Quarter Financial Data (Unaudited) [Abstract]
Interest rate on convertible senior notes	0.00%		0.00%		0.00%	0.00%		0.00%	0.00%
Income (Numerator) [Abstract]
Shares issuable related to our convertible notes			$ 777
Effect of Diluted Securities [Abstract]
Shares issuable related to our convertible notes (in shares)			10,936
0.125 Percent Convertible Senior Notes [Member]
Fourth Quarter Financial Data (Unaudited) [Abstract]
Interest rate on convertible senior notes	0.125%		0.125%		0.125%	0.125%	0.125%		0.125%
Income (Numerator) [Abstract]
Shares issuable related to our convertible notes			$ 716
Effect of Diluted Securities [Abstract]
Shares issuable related to our convertible notes (in shares)			6,590
1 Percent Convertible Senior Notes [Member]
Fourth Quarter Financial Data (Unaudited) [Abstract]
Interest rate on convertible senior notes	1.00%		1.00%		1.00%	1.00%	1.00%	1.00%	1.00%
Income (Numerator) [Abstract]
Shares issuable related to our convertible notes			$ 105
Effect of Diluted Securities [Abstract]
Shares issuable related to our convertible notes (in shares)			464
Stock Options [Member]
Effect of Diluted Securities [Abstract]
Shares issuable related to stock-based compensation (in shares)			46
Restricted Stock Awards [Member]
Effect of Diluted Securities [Abstract]
Shares issuable related to stock-based compensation (in shares)			1,065
Eplontersen Collaboration [Member]
Fourth Quarter Financial Data (Unaudited) [Abstract]
Revenue			$ 200,000
Metagenomi License Agreement [Member]
Fourth Quarter Financial Data (Unaudited) [Abstract]
Upfront payment	$ 80,000

[1] Revenue was lower in the three months ended December 31, 2022 compared to the same period in 2021 due to the $200 million we earned in the fourth quarter of 2021 from AstraZeneca to jointly develop and commercialize eplontersen.

[2] Operating expenses were higher in the three months ended December 31, 2022 compared to the same period in 2021 primarily due to the $80 million upfront payment we made for our collaboration with Metagenomi in the fourth quarter of 2022.

[3] Our net loss for the three months ended December 31, 2022 includes the $150.1 million gain we recognized from the sale and leaseback transaction for our headquarters in Carlsbad, California.

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

[5] 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.

[6] We had net income for the fourth quarter of 2021. As a result, we computed diluted net income per share using the weighted-average number of common shares and dilutive common equivalent shares outstanding during the period