Segment Operating Results (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Net Revenues	$ 402,515	$ 402,198	$ 1,336,597	$ 1,348,571
Operating Expenses	330,826	323,737	1,094,455	1,045,191
Other Expenses	8,003	8,117	42,424	22,392
Income Before Income from Equity Method Investments and Income Taxes	63,686	70,344	199,718	280,988
Income from Equity Method Investments	3,111	2,562	8,552	7,226
Pre-Tax Income	66,797	72,906	208,270	288,214
Identifiable Segment Assets	2,645,458	2,211,103	2,645,458	2,211,103	$ 2,598,613
Investment Banking [Member]
Segment Reporting Information [Line Items]
Net Revenues	385,463	388,012	1,294,493	1,305,586
Operating Expenses	318,655	311,697	1,057,926	1,008,985
Other Expenses	7,703	7,917	42,092	22,084
Income Before Income from Equity Method Investments and Income Taxes	59,105	68,398	194,475	274,517
Income from Equity Method Investments	570	282	1,171	756
Pre-Tax Income	59,675	68,680	195,646	275,273
Identifiable Segment Assets	2,460,068	2,018,087	2,460,068	2,018,087
Investment Management [Member]
Segment Reporting Information [Line Items]
Net Revenues	17,052	14,186	42,104	42,985
Operating Expenses	12,171	12,040	36,529	36,206
Other Expenses	300	200	332	308
Income Before Income from Equity Method Investments and Income Taxes	4,581	1,946	5,243	6,471
Income from Equity Method Investments	2,541	2,280	7,381	6,470
Pre-Tax Income	7,122	4,226	12,624	12,941
Identifiable Segment Assets	$ 185,390	$ 193,016	$ 185,390	$ 193,016