v3.26.1
FAIR VALUE MEASUREMENTS - Schedule of Quantitative Information Used as Level 3 Inputs (Details)
$ in Thousands
Jun. 30, 2026
USD ($)
$ / shares
Dec. 31, 2025
USD ($)
$ / shares
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fixed maturity investments trading $ 25,185,430 $ 24,884,323
Other investments, at fair value (Notes 3 and 4) 5,083,169 4,574,214
Other liabilities (2,983) (22,887)
Total assets and (liabilities) measured at fair value on a recurring basis using Level 3 inputs 36,060,780 35,928,451
Corporate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fixed maturity investments trading 9,916,723 8,528,828
Asset-backed    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fixed maturity investments trading 1,688,500 1,606,790
Significant Unobservable Inputs (Level 3)    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fixed maturity investments trading 311,464 154,115
Other investments, at fair value (Notes 3 and 4) 23,625 27,995
Other liabilities 0 (34)
Total assets and (liabilities) measured at fair value on a recurring basis using Level 3 inputs 335,089 182,076
Significant Unobservable Inputs (Level 3) | Corporate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fixed maturity investments trading 219,697 114,256
Significant Unobservable Inputs (Level 3) | Asset-backed    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fixed maturity investments trading 91,767 39,859
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) 23,625 27,995
Significant Unobservable Inputs (Level 3) | Discounted cash flow | Asset-backed    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fixed maturity investments trading 41,609 39,859
Significant Unobservable Inputs (Level 3) | Recent transaction price | Corporate    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fixed maturity investments trading   114,256
Significant Unobservable Inputs (Level 3) | Internal valuation model | Direct private equity investments    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Other investments, at fair value (Notes 3 and 4) 23,625 27,995
Significant Unobservable Inputs (Level 3) | Internal valuation model | Assumed reinsurance contract    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Other liabilities   (34)
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 $ 65,234 $ 182,076
Significant Unobservable Inputs (Level 3) | Discount rate | Discounted cash flow | Weighted Average or Actual | Asset-backed    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Unobservable measurement input | $ / shares 0.113 0.113
Significant Unobservable Inputs (Level 3) | Discount rate | Internal valuation model | Weighted Average or Actual | Direct private equity investments    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Significant observable and unobservable inputs 0.120 0.130
Significant Unobservable Inputs (Level 3) | Discount rate | Internal valuation model | Weighted Average or Actual | Assumed reinsurance contract    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Significant observable and unobservable inputs   0.037
Significant Unobservable Inputs (Level 3) | Liquidity discount | Internal valuation model | Weighted Average or Actual | Direct private equity investments    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Significant observable and unobservable inputs 0.100 0.100
Significant Unobservable Inputs (Level 3) | Net undiscounted cash flows | Internal valuation model | Weighted Average or Actual | Assumed reinsurance contract    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Significant observable and unobservable inputs   12,836,000
Significant Unobservable Inputs (Level 3) | Expected loss ratio | Internal valuation model | Weighted Average or Actual | Assumed reinsurance contract    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Significant observable and unobservable inputs   0