Investment Securities (Combined Financial Statements for Unconsolidated Subsidiaries Accounted for on Equity Method) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Schedule of Equity Method Investments [Line Items]
Investment income	$ 1,424,268	$ 1,441,009	$ 1,220,700
Expenses	965,348	998,658	769,542
Operating income	328,035	339,010	320,439
Net income	183,526	158,701	219,273
Investment securities	140,337	145,355
Cash and cash equivalents	268,600	224,580	193,411
Total assets	934,095	908,591
Total liabilities	1,675,909	1,716,468
Total liabilities and stockholders' deficiency	934,095	908,591
Unconsolidated Subsidiaries Accounted For As An Equity Method Investment
Schedule of Equity Method Investments [Line Items]
Investment income	4,713	3,209	1,574
Expenses	10,585	13,272	12,873
Operating income	(5,872)	(10,063)	(11,299)
Total net realized gain (loss) and net change in unrealized depreciation from investments	4,824	(84,466)	48,342
Net income	(1,048)	(94,529)	$ 37,043
Investment securities	290,916	299,389
Cash and cash equivalents	695	2,860
Other assets	38,471	87,507
Total assets	330,082	389,756
Other liabilities	159,858	159,246
Total liabilities	159,858	159,246
Partners’ capital	170,224	230,510
Total liabilities and stockholders' deficiency	$ 330,082	$ 389,756