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, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Disaggregation Of Revenue [Line Items]
Commissions	[1]	$ 165,075	$ 159,054	$ 499,983	$ 541,644
Investment banking	[1]	146,887	221,858	525,591	747,779
Revenue from contracts with customers	[1]	646,469	682,524	1,998,521	2,267,643
Capital Raising [Member]
Disaggregation Of Revenue [Line Items]
Investment banking	[1]	49,614	55,122	189,381	200,091
Advisory [Member]
Disaggregation Of Revenue [Line Items]
Investment banking	[1]	97,273	166,736	336,210	547,688
Asset Management [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers	[1]	333,127	300,557	968,960	973,457
Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers	[1]	1,380	1,055	3,987	4,763
Global Wealth Management [Member]
Disaggregation Of Revenue [Line Items]
Commissions	[1]	112,300	108,214	332,327	360,994
Investment banking	[1]	3,895	4,498	12,118	14,701
Revenue from contracts with customers	[1]	450,602	414,231	1,317,129	1,353,664
Global Wealth Management [Member] | Capital Raising [Member]
Disaggregation Of Revenue [Line Items]
Investment banking	[1]	3,895	4,498	12,118	14,701
Global Wealth Management [Member] | Asset Management [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers	[1]	333,088	300,540	968,863	973,396
Global Wealth Management [Member] | Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers	[1]	1,319	979	3,821	4,573
Institutional Group [Member]
Disaggregation Of Revenue [Line Items]
Commissions	[1]	52,775	50,840	167,656	180,650
Investment banking	[1]	142,992	217,360	513,473	733,078
Revenue from contracts with customers	[1]	195,823	268,217	681,243	913,789
Institutional Group [Member] | Capital Raising [Member]
Disaggregation Of Revenue [Line Items]
Investment banking	[1]	45,719	50,624	177,263	185,390
Institutional Group [Member] | Advisory [Member]
Disaggregation Of Revenue [Line Items]
Investment banking	[1]	97,273	166,736	336,210	547,688
Institutional Group [Member] | Asset Management [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers	[1]	39	17	97	61
Institutional Group [Member] | Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers	[1]	17		17
Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers	[1]	44	76	149	190
Other [Member] | Other [Member]
Disaggregation Of Revenue [Line Items]
Other	[1]	44	76	149	190
United States [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers	[1]	596,433	638,020	1,816,325	2,117,628
United States [Member] | Global Wealth Management [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers	[1]	450,602	414,231	1,317,129	1,353,664
United States [Member] | Institutional Group [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers	[1]	145,787	223,713	499,047	763,774
United States [Member] | Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers	[1]	44	76	149	190
United Kingdom [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers	[1]	31,240	29,987	99,844	101,342
United Kingdom [Member] | Institutional Group [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers	[1]	31,240	29,987	99,844	101,342
Canada [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers	[1]	8,601	7,920	38,738	25,043
Canada [Member] | Institutional Group [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers	[1]	8,601	7,920	38,738	25,043
Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers	[1]	10,195	6,597	43,614	23,630
Other [Member] | Institutional Group [Member]
Disaggregation Of Revenue [Line Items]
Revenue from contracts with customers	[1]	$ 10,195	$ 6,597	$ 43,614	$ 23,630

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