Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Assets:
Equity securities	$ 1,262,192	$ 1,203,788
Arbitrage trading account	1,035,000	1,123,000
Loans receivable	324,699	405,248
Carrying Value
Assets:
Fixed maturity securities	24,093,156	22,397,865
Equity securities	1,262,192	1,203,788
Arbitrage trading account	1,034,557	1,122,599
Loans receivable	324,365	405,453
Cash and cash equivalents	1,984,529	1,974,747
Trading account receivables from brokers and clearing organizations	138,891	60,327
Liabilities:
Due to broker	16,160	70,483
Trading account securities sold but not yet purchased	30,909	73,358
Senior notes and other debt	1,831,638	1,831,158
Subordinated debentures	1,010,168	1,009,808
Fair Value
Assets:
Fixed maturity securities	24,094,270	22,399,426
Equity securities	1,262,192	1,203,788
Arbitrage trading account	1,034,557	1,122,599
Loans receivable	324,699	405,248
Cash and cash equivalents	1,984,529	1,974,747
Trading account receivables from brokers and clearing organizations	138,891	60,327
Liabilities:
Due to broker	16,160	70,483
Trading account securities sold but not yet purchased	30,909	73,358
Senior notes and other debt	1,438,943	1,425,852
Subordinated debentures	$ 766,884	$ 805,864