Net Investment Income (Net Investment Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Net Investment Income [Line Items]
Gross investment income	$ 1,059,751	$ 789,106	$ 679,414
Investment expense	(6,916)	(9,921)	(7,796)
Net investment income	1,052,835	779,185	671,618
Fixed maturity securities, including cash and cash equivalents and loans receivable
Net Investment Income [Line Items]
Gross investment income	929,098	549,281	382,001
Investment funds
Net Investment Income [Line Items]
Gross investment income	16,743	145,099	220,014
Arbitrage trading account (1)
Net Investment Income [Line Items]
Gross investment income	69,369	45,213	37,676
Real estate
Net Investment Income [Line Items]
Gross investment income	(11,185)	(3,087)	7,703
Equity securities
Net Investment Income [Line Items]
Gross investment income	$ 55,726	$ 52,600	$ 32,020