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Fair Value Measurements and Financial Instruments - Narrative (Details) - USD ($)
$ in Millions
 1 Months Ended 12 Months Ended
Apr. 05, 2019
Nov. 30, 2021
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]          
Unrealized gain (loss) on equity securities still held     $ 60.1 $ 85.4 $ (104.4)
Restrictions on selling common stock, period     6 months    
Level 3 | BioCryst Pharmaceuticals, Inc.          
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]          
Number of shares purchased (in shares)   3,846,000      
Preferred Shares | Debt Securities          
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]          
Redemption price, percentage 200.00%        
Preferred shares, quarterly payments     $ 15.6    
Preferred shares, fixed payment amount     $ 250.0    
Change in control event, period     4 years    
Preferred shares, weighted average cost of capital     9.50% 8.30%  
Number of shares purchased (in shares) 2,495        
Preferred Shares | Maximum | Redemption, Period One          
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]          
Redemption price, percentage 200.00%        
Preferred Shares | Maximum | Redemption, Period One | Debt Securities          
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]          
Redemption price, percentage 200.00%