Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Assets:
Equity securities	$ 1,279,955	$ 1,185,894
Arbitrage trading account	609,000	944,000
Loans receivable	187,455	187,981
Carrying Value
Assets:
Fixed maturity securities	18,091,113	17,587,349
Equity securities	1,279,955	1,185,894
Arbitrage trading account	609,001	944,230
Loans receivable	194,944	193,002
Cash and cash equivalents	1,242,357	1,449,346
Trading account receivables from brokers and clearing organizations	583,970	233,863
Due from broker	17,207	3,609
Liabilities:
Senior notes and other debt	1,827,981	1,828,823
Subordinated debentures	1,008,551	1,008,371
Fair Value
Assets:
Fixed maturity securities	18,095,068	17,591,626
Equity securities	1,279,955	1,185,894
Arbitrage trading account	609,001	944,230
Loans receivable	187,455	187,981
Cash and cash equivalents	1,242,357	1,449,346
Trading account receivables from brokers and clearing organizations	583,970	233,863
Due from broker	17,207	3,609
Liabilities:
Senior notes and other debt	1,501,671	1,439,188
Subordinated debentures	$ 836,796	$ 805,600