Segment Operating Results (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Net Revenues	$ 687,865	$ 507,075	$ 1,350,175	$ 934,082
Operating Expenses	480,852	411,183	948,947	763,629
Other Expenses	0	9,163	7	34,421
Income Before Income from Equity Method Investments and Income Taxes	207,013	86,729	401,221	136,032
Income from Equity Method Investments	3,394	2,313	6,418	5,441
Pre-Tax Income	210,407	89,042	407,639	141,473
Identifiable Segment Assets	2,947,448	2,499,589	2,947,448	2,499,589	$ 3,370,888
Investment Banking [Member]
Segment Reporting Information [Line Items]
Net Revenues	670,820	495,374	1,318,105	909,030
Operating Expenses	468,160	399,476	924,686	739,271
Other Expenses	0	9,163	7	34,389
Income Before Income from Equity Method Investments and Income Taxes	202,660	86,735	393,412	135,370
Income from Equity Method Investments	549	65	718	601
Pre-Tax Income	203,209	86,800	394,130	135,971
Identifiable Segment Assets	2,775,859	2,358,662	2,775,859	2,358,662
Investment Management [Member]
Segment Reporting Information [Line Items]
Net Revenues	17,045	11,701	32,070	25,052
Operating Expenses	12,692	11,707	24,261	24,358
Other Expenses	0	0	0	32
Income Before Income from Equity Method Investments and Income Taxes	4,353	(6)	7,809	662
Income from Equity Method Investments	2,845	2,248	5,700	4,840
Pre-Tax Income	7,198	2,242	13,509	5,502
Identifiable Segment Assets	$ 171,589	$ 140,927	$ 171,589	$ 140,927