Investments - Quantitative Information about Level 3 Fair Value Measurements (Details) $ in Thousands	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ 17,870,206	$ 16,503,365
Collateralized debt obligations
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	42,146	50,364
Significant Unobservable Inputs (Level 3)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	496,879	528,447
Significant Unobservable Inputs (Level 3) | Private placement fixed maturities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	454,733
Significant Unobservable Inputs (Level 3) | Collateralized debt obligations
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ 42,146	$ 50,364
Significant Unobservable Inputs (Level 3) | Collateralized debt obligations | Discounted Cash Flows | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.1165
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	0.1165