Segment Operating Results (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Net Revenues	$ 415,327	$ 463,563
Operating Expenses	324,151	342,956
Other Expenses	7,366	8,058
Income Before Income from Equity Method Investments and Income Taxes	83,810	112,549
Income from Equity Method Investments	2,211	2,125
Pre-Tax Income	86,021	114,674
Identifiable Segment Assets	1,844,937	1,417,653	$ 2,125,667
Investment Banking [Member]
Segment Reporting Information [Line Items]
Net Revenues	401,188	450,200
Operating Expenses	311,910	331,683
Other Expenses	7,258	8,037
Income Before Income from Equity Method Investments and Income Taxes	82,020	110,480
Income from Equity Method Investments	255	0
Pre-Tax Income	82,275	110,480
Identifiable Segment Assets	1,650,115	1,148,662
Investment Management [Member]
Segment Reporting Information [Line Items]
Net Revenues	14,139	13,363
Operating Expenses	12,241	11,273
Other Expenses	108	21
Income Before Income from Equity Method Investments and Income Taxes	1,790	2,069
Income from Equity Method Investments	1,956	2,125
Pre-Tax Income	3,746	4,194
Identifiable Segment Assets	$ 194,822	$ 268,991