Fair Value Measurements - Schedule of Quantitative Information about Significant Unobservable Inputs in the Fair Value Measurement of Level 3 Assets (Details) $ in Thousands	Jun. 30, 2024 USD ($)	Dec. 31, 2023 USD ($)	Jun. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investment assets measured at fair value	$ 258,654	$ 288,955
Total Level 3 securities	571,389	551,689
Corporate securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Level 3 securities	293,713	297,332	$ 245,489	$ 187,980
CLO and other ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Level 3 securities	263,720	245,313	$ 201,926	$ 153,342
Valuation Technique, Discounted Cash Flow
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	312,735	262,734
Valuation Technique, Discounted Cash Flow | Corporate securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	154,075	135,524
Valuation Technique, Discounted Cash Flow | CLO and other ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	$ 158,660	$ 127,210
Valuation Technique, Discounted Cash Flow | Illiquidity Spread | Minimum | Corporate securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale, measurement input	(0.044)	(0.044)
Valuation Technique, Discounted Cash Flow | Illiquidity Spread | Minimum | CLO and other ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale, measurement input	0.0001	0.0001
Valuation Technique, Discounted Cash Flow | Illiquidity Spread | Maximum | Corporate securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale, measurement input	0.053	0.053
Valuation Technique, Discounted Cash Flow | Illiquidity Spread | Maximum | CLO and other ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale, measurement input	0.196	0.196
Valuation Technique, Discounted Cash Flow | Illiquidity Spread | Weighted Average | Corporate securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale, measurement input	0.018	0.019
Valuation Technique, Discounted Cash Flow | Illiquidity Spread | Weighted Average | CLO and other ABS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale, measurement input	0.025	0.024