Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Assets:
Equity securities	$ 1,239,712	$ 1,185,894
Arbitrage trading account	724,000	944,000
Loans receivable	177,609	187,981
Carrying Value
Assets:
Fixed maturity securities	18,055,623	17,587,349
Equity securities	1,239,712	1,185,894
Arbitrage trading account	723,967	944,230
Loans receivable	181,562	193,002
Cash and cash equivalents	1,823,558	1,449,346
Trading account receivables from brokers and clearing organizations	484,457	233,863
Due from broker	0	3,609
Liabilities:
Due to broker	100,795	0
Senior notes and other debt	1,827,080	1,828,823
Subordinated debentures	1,008,730	1,008,371
Fair Value
Assets:
Fixed maturity securities	18,058,505	17,591,626
Equity securities	1,239,712	1,185,894
Arbitrage trading account	723,967	944,230
Loans receivable	177,609	187,981
Cash and cash equivalents	1,823,558	1,449,346
Trading account receivables from brokers and clearing organizations	484,457	233,863
Due from broker	0	3,609
Liabilities:
Due to broker	100,795	0
Senior notes and other debt	1,444,422	1,439,188
Subordinated debentures	$ 870,898	$ 805,600