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Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
Assets:
Equity securities	$ 1,382,432	$ 1,203,788
Arbitrage trading account	1,070,000	1,123,000
Loans receivable	327,102	405,248
Carrying Value
Assets:
Fixed maturity securities	24,947,949	22,397,865
Equity securities	1,382,432	1,203,788
Arbitrage trading account	1,070,304	1,122,599
Loans receivable	326,855	405,453
Cash and cash equivalents	2,404,019	1,974,747
Trading account receivables from brokers and clearing organizations	113,330	60,327
Liabilities:
Due to broker	130,723	70,483
Trading account securities sold but not yet purchased	34,509	73,358
Senior notes and other debt	1,829,511	1,831,158
Subordinated debentures	1,010,347	1,009,808
Fair Value
Assets:
Fixed maturity securities	24,949,094	22,399,426
Equity securities	1,382,432	1,203,788
Arbitrage trading account	1,070,304	1,122,599
Loans receivable	327,102	405,248
Cash and cash equivalents	2,404,019	1,974,747
Trading account receivables from brokers and clearing organizations	113,330	60,327
Liabilities:
Due to broker	130,723	70,483
Trading account securities sold but not yet purchased	34,509	73,358
Senior notes and other debt	1,482,612	1,425,852
Subordinated debentures	$ 834,836	$ 805,864

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