Revenues From Contracts With Customers (Revenues from Contracts with Customers Disaggregated by Major Business Activity and Primary Geographic Regions) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020		Dec. 31, 2019	Dec. 31, 2018
Disaggregation Of Revenue [Line Items]
Commissions		$ 760,627		$ 667,494
Investment banking		952,308		817,421
Revenue from contracts with customers		2,678,888		2,352,237
Other		48,529		19,287
Capital Raising [Member]
Disaggregation Of Revenue [Line Items]
Investment banking		524,157	[1]	369,442
Advisory Fees [Member]
Disaggregation Of Revenue [Line Items]
Investment banking		428,151	[1]	447,979
Asset Management [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers		917,424		848,035	$ 806,175
Global Wealth Management [Member]
Disaggregation Of Revenue [Line Items]
Commissions		513,247		477,401
Investment banking		36,024		37,915
Revenue from contracts with customers		1,512,062		1,379,730
Other		45,438		16,437
Global Wealth Management [Member] | Capital Raising [Member]
Disaggregation Of Revenue [Line Items]
Investment banking		36,005	[1]	37,915
Global Wealth Management [Member] | Advisory Fees [Member]
Disaggregation Of Revenue [Line Items]
Investment banking	[1]	19
Global Wealth Management [Member] | Asset Management [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers		917,353		847,977
Institutional Group [Member]
Disaggregation Of Revenue [Line Items]
Commissions		247,380		190,093
Investment banking		916,284		779,506
Revenue from contracts with customers		1,163,735		969,657
Institutional Group [Member] | Capital Raising [Member]
Disaggregation Of Revenue [Line Items]
Investment banking		488,152	[1]	331,527
Institutional Group [Member] | Advisory Fees [Member]
Disaggregation Of Revenue [Line Items]
Investment banking		428,132	[1]	447,979
Institutional Group [Member] | Asset Management [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers		71		58
Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers		3,091		2,850
Other		3,091		2,850
United States [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers		2,455,425		2,205,338
United States [Member] | Global Wealth Management [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers		1,512,062		1,379,730
United States [Member] | Institutional Group [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers		940,272		822,758
United States [Member] | Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers		3,091		2,850
United Kingdom [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers		143,960		135,529
United Kingdom [Member] | Institutional Group [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers		143,960		135,529
Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers		79,503		11,370
Other [Member] | Institutional Group [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers		$ 79,503		$ 11,370

[1] Excludes revenues not derived from contracts with customers in the Other segment.