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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.

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