Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Assets:
Equity securities	$ 1,090,347	$ 1,185,894
Arbitrage trading account	938,000	944,000
Loans receivable	198,244	187,981
Carrying Value
Assets:
Fixed maturity securities	20,178,308	17,587,349
Equity securities	1,090,347	1,185,894
Arbitrage trading account	938,049	944,230
Loans receivable	201,271	193,002
Cash and cash equivalents	1,363,195	1,449,346
Trading accounts receivable from brokers and clearing organizations	303,614	233,863
Due from broker	36,747	3,609
Liabilities:
Trading account securities sold but not yet purchased	9,357	0
Carrying Value | Total senior notes and other debt
Liabilities:
Long-term debt fair value	1,827,951	1,828,823
Carrying Value | Total subordinated debentures
Liabilities:
Long-term debt fair value	1,009,090	1,008,371
Fair Value
Assets:
Fixed maturity securities	20,181,547	17,591,626
Equity securities	1,090,347	1,185,894
Arbitrage trading account	938,049	944,230
Loans receivable	198,244	187,981
Cash and cash equivalents	1,363,195	1,449,346
Trading accounts receivable from brokers and clearing organizations	303,614	233,863
Due from broker	36,747	3,609
Liabilities:
Trading account securities sold but not yet purchased	9,357	0
Fair Value | Total senior notes and other debt
Liabilities:
Long-term debt fair value	1,480,076	1,439,188
Fair Value | Total subordinated debentures
Liabilities:
Long-term debt fair value	$ 929,598	$ 805,600