Investment Securities (Combined Financial Statements for Unconsolidated Subsidiaries Accounted for on Equity Method) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Schedule of Equity Method Investments [Line Items]
Investment securities at fair value	$ 145,355				$ 178,776				$ 145,355	$ 178,776
Cash and cash equivalents	224,580				193,411				224,580	193,411	$ 258,421
Total assets	908,591				871,087				908,591	871,087
Total liabilities	1,716,468				1,712,640				1,716,468	1,712,640
Total liabilities and stockholders' deficiency	908,591				871,087				908,591	871,087
Investment income	363,770	$ 377,995	$ 387,202	$ 312,042	313,673	$ 298,485	$ 337,554	$ 270,988	1,441,009	1,220,700	1,228,682
Total cost of sales									998,658	769,542	819,602
Operating income	89,272	$ 83,901	$ 90,711	$ 75,126	68,556	$ 82,015	$ 93,893	$ 75,975	339,010	320,439	294,428
Net income									158,701	219,273	92,938
Unconsolidated Subsidiaries Accounted For As An Equity Method Investment
Schedule of Equity Method Investments [Line Items]
Investment securities at fair value	299,389				493,705				299,389	493,705
Cash and cash equivalents	2,860				44,644				2,860	44,644
Other assets	87,507				14,151				87,507	14,151
Total assets	389,756				552,500				389,756	552,500
Other liabilities	159,246				214,607				159,246	214,607
Total liabilities	159,246				214,607				159,246	214,607
Partners’ capital	230,510				337,893				230,510	337,893
Total liabilities and stockholders' deficiency	$ 389,756				$ 552,500				389,756	552,500
Investment income									3,209	1,574	1,779
Total cost of sales									13,272	12,873	9,300
Operating income									(10,063)	(11,299)	(7,521)
Total net realized gain (loss) and net change in unrealized depreciation from investments									(84,466)	48,342	123,381
Net income									$ (94,529)	$ 37,043	$ 115,860