Investments - Quantitative Information about Level 3 Fair Value Measurements (Details) $ in Thousands	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ 17,155,012	$ 17,870,206
Collateralized debt obligations
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	42,866	42,146
Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	474,114	496,879
Significant Unobservable Inputs (Level 3) | Private placement fixed maturities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	420,065
Significant Unobservable Inputs (Level 3) | Collateralized debt obligations
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ 42,866	$ 42,146
Significant Unobservable Inputs (Level 3) | Collateralized debt obligations | Discounted Cash Flows | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.1175
Significant Unobservable Inputs (Level 3) | Collateralized debt obligations | Discounted Cash Flows | Discount rate | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.1175
Significant Unobservable Inputs (Level 3) | Asset-backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ 11,183