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Other Consolidated Financial Statement Detail - Narrative (Details) - USD ($) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2018 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Business Acquisition [Line Items] |  |  |  |
Increase to goodwill |  | $ 0 | $ 117,500,000 |
Unrealized gain (loss) on investments |  | (681,800,000) | 150,100,000 |
Realized investment gains (losses) |  | 12,100,000 | 50,000,000.0 |
Unrealized gains (losses) recognized during the period on equity securities |  | 681,800,000 | 150,100,000 | $ 128,500,000
Other long-term liabilities |  | 1,329,600,000 | 1,348,900,000 |
Accrued income taxes |  | 709,900,000 | 803,300,000 |
Denali and Sangamo |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Unrealized gains (losses) recognized during the period on equity securities |  | 703,900,000 |  |
Solothurn |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Construction in progress |  | 12,400,000 | $ 50,000,000.0 |
Fumarate | Fumapharm AG | Twenty billion |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Increase to goodwill | $ 300,000,000.0 |  |  |
Cumulative sales level | 20,000,000,000.0 |  |  | 20,000,000,000.0
Fumarate | Fumapharm AG | Each additional one billion up to twenty billion |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Cumulative sales level | $ 20,000,000,000.0 | $ 20,000,000,000.0 |  | $ 20,000,000,000.0

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