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Investments - Investment in NGP (Additional Information) (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2023
Sep. 30, 2022
Sep. 30, 2023
Sep. 30, 2022
Schedule of Equity Method Investments [Line Items]        
Performance allocations, percentage (percent)     47.50%  
Amortization period of basis difference     10 years  
Investment in NGP Management        
Schedule of Equity Method Investments [Line Items]        
Performance allocations, percentage (percent)     47.50%  
NGP Management        
Schedule of Equity Method Investments [Line Items]        
Net investment earnings related to performance allocations $ 51.2 $ 81.6 $ 87.7 $ 532.2
Net investment (losses) earnings related to principal investment income $ 6.7 $ 9.6 $ 10.6 $ 43.0
Minimum        
Schedule of Equity Method Investments [Line Items]        
Performance allocations, carry funds, percentage (percent)     40.00%  
Minimum | NGP Management        
Schedule of Equity Method Investments [Line Items]        
Management fee, percentage of commitments (percent)     1.00%  
Management fee, percentage of invested capital (percent)     0.50%  
Maximum        
Schedule of Equity Method Investments [Line Items]        
Performance allocations, carry funds, percentage (percent)     42.75%  
Maximum | NGP Management        
Schedule of Equity Method Investments [Line Items]        
Management fee, percentage of commitments (percent)     2.00%  
Management fee, percentage of invested capital (percent)     2.00%  
Management Fee Related Revenues | Investment in NGP Management        
Schedule of Equity Method Investments [Line Items]        
Management fee-related revenues, allocation percentage (percent)     55.00%