Segment Operating Results (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Net Revenues	$ 662,310	$ 427,007
Operating Expenses	468,095	352,446
Other Expenses	7	25,258
Income Before Income from Equity Method Investments and Income Taxes	194,208	49,303
Income from Equity Method Investments	3,024	3,128
Pre-Tax Income	197,232	52,431
Identifiable Segment Assets	2,725,913	2,221,552	$ 3,370,888
Investment Banking [Member]
Segment Reporting Information [Line Items]
Net Revenues	647,285	413,656
Operating Expenses	456,526	339,795
Other Expenses	7	25,226
Income Before Income from Equity Method Investments and Income Taxes	190,752	48,635
Income from Equity Method Investments	169	536
Pre-Tax Income	190,921	49,171
Identifiable Segment Assets	2,576,598	2,070,887
Investment Management [Member]
Segment Reporting Information [Line Items]
Net Revenues	15,025	13,351
Operating Expenses	11,569	12,651
Other Expenses	0	32
Income Before Income from Equity Method Investments and Income Taxes	3,456	668
Income from Equity Method Investments	2,855	2,592
Pre-Tax Income	6,311	3,260
Identifiable Segment Assets	$ 149,315	$ 150,665