v3.26.3
FAIR VALUE MEASUREMENTS - Schedule of Quantitative Information Used as Level 3 Inputs (Details)
$ in Thousands
Sep. 30, 2026
USD ($)
$ / shares
Dec. 31, 2025
USD ($)
$ / shares
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fixed maturity investments trading $ 25,203,247 $ 24,884,323
Other investments, at fair value (Notes 3 and 4) 5,047,962 4,574,214
Other liabilities (14,569) (22,887)
Total assets and (liabilities) measured at fair value on a recurring basis using Level 3 inputs 36,013,792 35,928,451
Corporate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fixed maturity investments trading 9,807,924 8,528,828
Asset-backed    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fixed maturity investments trading 1,357,970 1,606,790
Significant Unobservable Inputs (Level 3)    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fixed maturity investments trading 383,805 154,115
Other investments, at fair value (Notes 3 and 4) 24,562 27,995
Other liabilities 0 (34)
Total assets and (liabilities) measured at fair value on a recurring basis using Level 3 inputs 408,367 182,076
Significant Unobservable Inputs (Level 3) | Unobservable Input Developed By The Company    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Total assets and (liabilities) measured at fair value on a recurring basis using Level 3 inputs 60,330 182,076
Significant Unobservable Inputs (Level 3) | Corporate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fixed maturity investments trading 246,947 114,256
Significant Unobservable Inputs (Level 3) | Corporate | Recent transaction price    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fixed maturity investments trading   114,256
Significant Unobservable Inputs (Level 3) | Asset-backed    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fixed maturity investments trading 136,858 39,859
Significant Unobservable Inputs (Level 3) | Asset-backed | Discounted cash flow    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fixed maturity investments trading $ 35,768 $ 39,859
Significant Unobservable Inputs (Level 3) | Asset-backed | Discounted cash flow | Weighted Average or Actual | Discount rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Unobservable measurement input | $ / shares 0.113 0.113
Significant Unobservable Inputs (Level 3) | Direct private equity investments    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Other investments, at fair value (Notes 3 and 4) $ 24,562 $ 27,995
Significant Unobservable Inputs (Level 3) | Direct private equity investments | Internal valuation model    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Other investments, at fair value (Notes 3 and 4) $ 24,562 $ 27,995
Significant Unobservable Inputs (Level 3) | Direct private equity investments | Internal valuation model | Weighted Average or Actual | Discount rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Significant observable and unobservable inputs 0.120 0.130
Significant Unobservable Inputs (Level 3) | Direct private equity investments | Internal valuation model | Weighted Average or Actual | Liquidity discount    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Significant observable and unobservable inputs 0.100 0.100
Significant Unobservable Inputs (Level 3) | Assumed reinsurance contract | Internal valuation model    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Other liabilities   $ (34)
Significant Unobservable Inputs (Level 3) | Assumed reinsurance contract | Internal valuation model | Weighted Average or Actual | Discount rate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Significant observable and unobservable inputs   0.037
Significant Unobservable Inputs (Level 3) | Assumed reinsurance contract | Internal valuation model | Weighted Average or Actual | Net undiscounted cash flows    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Significant observable and unobservable inputs   12,836,000
Significant Unobservable Inputs (Level 3) | Assumed reinsurance contract | Internal valuation model | Weighted Average or Actual | Expected loss ratio    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Significant observable and unobservable inputs   0