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Financial Instruments Financial Instruments (Details Textual 2) - USD ($) $ / shares in Units, shares in Millions, $ in Millions | 1 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Nov. 30, 2020 | Sep. 30, 2020 | Feb. 29, 2020 | Sep. 30, 2021 | Dec. 31, 2020
Sage Therapeutics Inc. |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |
Global licensing collaboration agreement, amount, shares purchased (in shares) | $ 650.0 |  |  |  |
Global licensing collaboration agreement, shares, purchased (in shares) | 6.2 |  |  |  |
Global licensing collaboration agreement, purchase price per share (in usd per share) | $ 104.14 |  |  |  |
Dividend yield percentage |  |  |  | 0.00% |
Sangamo Therapeutics, Inc. Agreement |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |
Global licensing collaboration agreement, amount, shares purchased (in shares) |  |  | $ 225.0 |  |
Global licensing collaboration agreement, shares, purchased (in shares) |  |  | 24.0 |  |
Global licensing collaboration agreement, shares purchased per share (in usd per share) |  |  | $ 9.21 |  |
Denali Therapeutics |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |
Global licensing collaboration agreement, amount, shares purchased (in shares) |  | $ 465.0 |  |  |
Global licensing collaboration agreement, shares purchased per share (in usd per share) |  | $ 34.94 |  |  |
Strategic Investments |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |
Strategic investment portfolio |  |  |  | $ 1,222.3 |
Other noncurrent assets | Strategic Investments |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |
Strategic investment portfolio |  |  |  |  | $ 2,024.6
Denali Therapeutics |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |
Investment in common stock, shares purchased |  | 13.0 |  |  |
Dividend yield percentage |  | 0.00% |  |  |
Sangamo |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |
Investment in common stock, shares purchased |  |  |  | 12.0 |
Dividend yield percentage |  |  | 0.00% |  |

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