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Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Assets:
Equity securities	$ 1,203,788	$ 1,090,347
Arbitrage trading account	1,123,000	938,000
Loans receivable	405,248	198,244
Liabilities:
Due to broker	70,483	0
Carrying Value
Assets:
Fixed maturity securities	22,397,865	20,178,308
Equity securities	1,203,788	1,090,347
Arbitrage trading account	1,122,599	938,049
Loans receivable	405,453	201,271
Cash and cash equivalents	1,974,747	1,363,195
Trading accounts receivable from brokers and clearing organizations	60,327	303,614
Due from broker	0	36,747
Liabilities:
Trading account securities sold but not yet purchased	73,358	9,357
Carrying Value | Total senior notes and other debt
Liabilities:
Long-term debt fair value	1,831,158	1,827,951
Carrying Value | Total subordinated debentures
Liabilities:
Long-term debt fair value	1,009,808	1,009,090
Fair Value
Assets:
Fixed maturity securities	22,399,426	20,181,547
Equity securities	1,203,788	1,090,347
Arbitrage trading account	1,122,599	938,049
Loans receivable	405,248	198,244
Cash and cash equivalents	1,974,747	1,363,195
Trading accounts receivable from brokers and clearing organizations	60,327	303,614
Due from broker	0	36,747
Liabilities:
Trading account securities sold but not yet purchased	73,358	9,357
Fair Value | Total senior notes and other debt
Liabilities:
Long-term debt fair value	1,425,852	1,480,076
Fair Value | Total subordinated debentures
Liabilities:
Long-term debt fair value	$ 805,864	$ 929,598

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