Segment Operating Results (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Net Revenues	$ 507,075	$ 531,046	$ 934,082	$ 946,373
Operating Expenses	411,183	397,303	763,629	721,454
Other Expenses	9,163	6,909	34,421	14,275
Income Before Income from Equity Method Investments and Income Taxes	86,729	126,834	136,032	210,644
Income from Equity Method Investments	2,313	2,453	5,441	4,664
Pre-Tax Income	89,042	129,287	141,473	215,308
Identifiable Segment Assets	2,499,589	1,939,749	2,499,589	1,939,749	$ 2,598,613
Investment Banking [Member]
Segment Reporting Information [Line Items]
Net Revenues	495,374	516,386	909,030	917,574
Operating Expenses	399,476	385,378	739,271	697,288
Other Expenses	9,163	6,909	34,389	14,167
Income Before Income from Equity Method Investments and Income Taxes	86,735	124,099	135,370	206,119
Income from Equity Method Investments	65	219	601	474
Pre-Tax Income	86,800	124,318	135,971	206,593
Identifiable Segment Assets	2,358,662	1,749,339	2,358,662	1,749,339
Investment Management [Member]
Segment Reporting Information [Line Items]
Net Revenues	11,701	14,660	25,052	28,799
Operating Expenses	11,707	11,925	24,358	24,166
Other Expenses	0	0	32	108
Income Before Income from Equity Method Investments and Income Taxes	(6)	2,735	662	4,525
Income from Equity Method Investments	2,248	2,234	4,840	4,190
Pre-Tax Income	2,242	4,969	5,502	8,715
Identifiable Segment Assets	$ 140,927	$ 190,410	$ 140,927	$ 190,410