Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Assets:
Equity securities	$ 941,243	$ 625,667
Arbitrage trading account	1,180,000	341,000
Loans receivable	116,534	86,596
Liabilities:
Due to broker	53,636	0
Due to broker	53,636	0
Carrying Value
Assets:
Fixed maturity securities	16,602,673	14,159,369
Equity securities	941,243	625,667
Arbitrage trading account	1,179,606	341,473
Loans receivable	115,172	84,913
Cash and cash equivalents	1,568,843	2,372,366
Trading accounts receivable from brokers and clearing organizations	0	524,727
Due from broker	20,448	2,585
Liabilities:
Trading account securities sold but not yet purchased	1,169	10,048
Carrying Value | Total senior notes and other debt
Liabilities:
Long-term debt fair value	2,259,416	1,623,025
Carrying Value | Total subordinated debentures
Liabilities:
Long-term debt fair value	1,007,652	1,102,309
Fair Value
Assets:
Fixed maturity securities	16,614,118	14,173,629
Equity securities	941,243	625,667
Arbitrage trading account	1,179,606	341,473
Loans receivable	116,534	86,596
Cash and cash equivalents	1,568,843	2,372,366
Trading accounts receivable from brokers and clearing organizations	0	524,727
Due from broker	20,448	2,585
Liabilities:
Trading account securities sold but not yet purchased	1,169	10,048
Fair Value | Total senior notes and other debt
Liabilities:
Long-term debt fair value	2,526,630	1,892,444
Fair Value | Total subordinated debentures
Liabilities:
Long-term debt fair value	$ 1,095,600	$ 1,202,842