Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Assets:
Equity securities	$ 1,185,894	$ 941,243
Arbitrage trading account	944,000	1,180,000
Loans receivable	187,981	116,534
Liabilities:
Due to broker	0	53,636
Due to broker	0	53,636
Carrying Value
Assets:
Fixed maturity securities	17,587,349	16,602,673
Equity securities	1,185,894	941,243
Arbitrage trading account	944,230	1,179,606
Loans receivable	193,002	115,172
Cash and cash equivalents	1,449,346	1,568,843
Trading accounts receivable from brokers and clearing organizations	233,863	0
Due from broker	3,609	20,448
Liabilities:
Trading account securities sold but not yet purchased	0	1,169
Carrying Value | Total senior notes and other debt
Liabilities:
Long-term debt fair value	1,828,823	2,259,416
Carrying Value | Total subordinated debentures
Liabilities:
Long-term debt fair value	1,008,371	1,007,652
Fair Value
Assets:
Fixed maturity securities	17,591,626	16,614,118
Equity securities	1,185,894	941,243
Arbitrage trading account	944,230	1,179,606
Loans receivable	187,981	116,534
Cash and cash equivalents	1,449,346	1,568,843
Trading accounts receivable from brokers and clearing organizations	233,863	0
Due from broker	3,609	20,448
Liabilities:
Trading account securities sold but not yet purchased	0	1,169
Fair Value | Total senior notes and other debt
Liabilities:
Long-term debt fair value	1,439,188	2,526,630
Fair Value | Total subordinated debentures
Liabilities:
Long-term debt fair value	$ 805,600	$ 1,095,600