Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Assets:
Equity securities	$ 1,182,061	$ 1,185,894
Arbitrage trading account	825,000	944,000
Loans receivable	174,300	187,981
Carrying Value
Assets:
Fixed maturity securities	19,035,305	17,587,349
Equity securities	1,182,061	1,185,894
Arbitrage trading account	825,049	944,230
Loans receivable	177,750	193,002
Cash and cash equivalents	1,646,074	1,449,346
Trading account receivables from brokers and clearing organizations	401,982	233,863
Due from broker	0	3,609
Liabilities:
Due to broker	5,118	0
Trading account securities sold but not yet purchased	7,538	0
Senior notes and other debt	1,828,046	1,828,823
Subordinated debentures	1,008,910	1,008,371
Fair Value
Assets:
Fixed maturity securities	19,037,149	17,591,626
Equity securities	1,182,061	1,185,894
Arbitrage trading account	825,049	944,230
Loans receivable	174,300	187,981
Cash and cash equivalents	1,646,074	1,449,346
Trading account receivables from brokers and clearing organizations	401,982	233,863
Due from broker	0	3,609
Liabilities:
Due to broker	5,118	0
Trading account securities sold but not yet purchased	7,538	0
Senior notes and other debt	1,321,014	1,439,188
Subordinated debentures	$ 786,798	$ 805,600