Segment Operating Results (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net Revenues	$ 387,247	$ 257,713
Operating Expenses	294,897	206,478
Other Expenses	(18,979)	35,110
Income Before Income from Equity Method Investments and Income Taxes	111,329	16,125
Income (Loss) from Equity Method Investments	1,610	1,287
Pre-Tax Income	112,939	17,412
Identifiable Segment Assets	1,432,762	1,284,677	$ 1,662,346
Investment Banking [Member]
Segment Reporting Information [Line Items]
Net Revenues	370,770	239,713
Operating Expenses	281,592	192,264
Other Expenses	(18,979)	35,028
Income Before Income from Equity Method Investments and Income Taxes	108,157	12,421
Income (Loss) from Equity Method Investments	(149)	(272)
Pre-Tax Income	108,008	12,149
Identifiable Segment Assets	1,077,509	940,859
Investment Management [Member]
Segment Reporting Information [Line Items]
Net Revenues	16,477	18,000
Operating Expenses	13,305	14,214
Other Expenses	0	82
Income Before Income from Equity Method Investments and Income Taxes	3,172	3,704
Income (Loss) from Equity Method Investments	1,759	1,559
Pre-Tax Income	4,931	5,263
Identifiable Segment Assets	$ 355,253	$ 343,818