Segment Operating Results (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Net Revenues	$ 402,198	$ 381,259	$ 1,348,571	$ 1,293,299
Operating Expenses	323,737	298,831	1,045,191	979,602
Other Expenses	8,117	7,888	22,392	21,826
Income Before Income from Equity Method Investments and Income Taxes	70,344	74,540	280,988	291,871
Income from Equity Method Investments	2,562	2,298	7,226	6,842
Pre-Tax Income	72,906	76,838	288,214	298,713
Identifiable Segment Assets	2,211,103	1,705,607	2,211,103	1,705,607	$ 2,125,667
Investment Banking [Member]
Segment Reporting Information [Line Items]
Net Revenues	388,012	366,834	1,305,586	1,252,709
Operating Expenses	311,697	287,809	1,008,985	946,629
Other Expenses	7,917	7,888	22,084	21,805
Income Before Income from Equity Method Investments and Income Taxes	68,398	71,137	274,517	284,275
Income from Equity Method Investments	282	0	756	297
Pre-Tax Income	68,680	71,137	275,273	284,572
Identifiable Segment Assets	2,018,087	1,294,106	2,018,087	1,294,106
Investment Management [Member]
Segment Reporting Information [Line Items]
Net Revenues	14,186	14,425	42,985	40,590
Operating Expenses	12,040	11,022	36,206	32,973
Other Expenses	200	0	308	21
Income Before Income from Equity Method Investments and Income Taxes	1,946	3,403	6,471	7,596
Income from Equity Method Investments	2,280	2,298	6,470	6,545
Pre-Tax Income	4,226	5,701	12,941	14,141
Identifiable Segment Assets	$ 193,016	$ 411,501	$ 193,016	$ 411,501