Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Value of input used to measure investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Fair value portion of other assets.

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Fair Value (Quantitative Information about Significant Unobservable Inputs in the Fair Value Measurement of Level 3 Assets) (Details) $ in Thousands	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investment assets measured at fair value	$ 288,955	$ 207,936
Total Level 3 Securities	551,689	349,255	$ 251,282
Corporate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Level 3 Securities	297,332	187,980	114,127
Collateralized Loan Obligations and Other Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Level 3 Securities	245,313	153,342	$ 124,909
Valuation Technique, Discounted Cash Flow
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	262,734	141,319
Valuation Technique, Discounted Cash Flow \| Corporate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	135,524	81,867
Valuation Technique, Discounted Cash Flow \| Collateralized Loan Obligations and Other Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	$ 127,210	$ 59,452
Valuation Technique, Discounted Cash Flow \| Measurement Input, Credit Spread \| Minimum [Member] \| Corporate Securities [Member]
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 \| Measurement Input, Credit Spread \| Minimum [Member] \| Collateralized Loan Obligations and Other Asset-Backed Securities [Member]
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 \| Measurement Input, Credit Spread \| Maximum [Member] \| Corporate Securities [Member]
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 \| Measurement Input, Credit Spread \| Maximum [Member] \| Collateralized Loan Obligations and Other Asset-Backed Securities [Member]
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 \| Measurement Input, Credit Spread \| Weighted Average \| Corporate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale, Measurement Input	0.019	0.013
Valuation Technique, Discounted Cash Flow \| Measurement Input, Credit Spread \| Weighted Average \| Collateralized Loan Obligations and Other Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale, Measurement Input	0.024	0.025