Revenues from Contracts with Customers (Revenues from Contracts with Customers Disaggregated by Major Business Activity and Primary Geographic Regions) (Details) - USD ($) $ in Thousands		3 Months Ended				9 Months Ended
		Sep. 30, 2021		Sep. 30, 2020		Sep. 30, 2021		Sep. 30, 2020
Disaggregation Of Revenue [Line Items]
Commissions		$ 189,239	[1]	$ 172,654	[1]	$ 598,432	[1]	$ 560,780
Investment banking		372,279		218,134		1,088,010		614,637
Revenue from contracts with customers		880,472		636,899		2,604,651		1,875,321
Other		5,092		15,329		30,331		32,408
Capital Raising [Member]
Disaggregation Of Revenue [Line Items]
Investment banking	[1]	164,061		137,292		542,645		359,885
Advisory Fees [Member]
Disaggregation Of Revenue [Line Items]
Investment banking	[1]	208,218		80,842		545,365		254,752
Asset Management [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers		313,862		230,782		887,878		667,496
Global Wealth Management [Member]
Disaggregation Of Revenue [Line Items]
Commissions		133,998	[1]	120,600	[1]	421,156	[1]	373,653
Investment banking		11,580		8,113		37,027		26,462
Revenue from contracts with customers		464,622		374,013		1,374,529		1,097,665
Other		5,206		14,535		28,552		30,104
Global Wealth Management [Member] | Capital Raising [Member]
Disaggregation Of Revenue [Line Items]
Investment banking	[1]	11,580		8,113		37,027		26,443
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		313,838		230,765		887,794		667,446
Institutional Group [Member]
Disaggregation Of Revenue [Line Items]
Commissions		55,241	[1]	52,054	[1]	177,276	[1]	187,127
Investment banking		360,699		210,021		1,050,983		588,175
Revenue from contracts with customers		415,964		262,092		1,228,343		775,352
Institutional Group [Member] | Capital Raising [Member]
Disaggregation Of Revenue [Line Items]
Investment banking	[1]	152,481		129,179		505,618		333,442
Institutional Group [Member] | Advisory Fees [Member]
Disaggregation Of Revenue [Line Items]
Investment banking	[1]	208,218		80,842		545,365		254,733
Institutional Group [Member] | Asset Management [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers		24		17		84		50
Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers		(114)		794		1,779		2,304
Other		(114)		794		1,779		2,304
United States [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers		812,595		583,948		2,372,737		1,709,297
United States [Member] | Global Wealth Management [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers		464,622		374,013		1,374,529		1,097,665
United States [Member] | Institutional Group [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers		348,087		209,141		996,429		609,328
United States [Member] | Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers		(114)		794		1,779		2,304
United Kingdom [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers		46,267		30,959		137,482		110,053
United Kingdom [Member] | Institutional Group [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers		46,267		30,959		137,482		110,053
Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers		8,522		10,859		30,287		28,731
Other [Member] | Institutional Group [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers		8,522		10,859		30,287		28,731
Canada [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers		13,088		11,133		64,145		27,240
Canada [Member] | Institutional Group [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers		$ 13,088		$ 11,133		$ 64,145		$ 27,240

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