Segment, Geographic and Product Information - Product Information Regarding Revenues (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Segment Reporting Information [Line Items]
Total revenues	$ 435,756	$ 512,450	$ 942,220	$ 1,080,026
Rates
Segment Reporting Information [Line Items]
Total revenues	137,129	136,474	295,938	298,267
FX
Segment Reporting Information [Line Items]
Total revenues	74,347	72,807	154,372	156,240
Energy and commodities
Segment Reporting Information [Line Items]
Total revenues	66,687	74,735	149,082	150,603
Credit
Segment Reporting Information [Line Items]
Total revenues	61,257	72,609	145,165	162,656
Equities
Segment Reporting Information [Line Items]
Total revenues	58,291	60,825	125,419	131,287
Insurance
Segment Reporting Information [Line Items]
Total revenues	0	54,315	0	106,695
Total brokerage revenues
Segment Reporting Information [Line Items]
Total revenues	397,711	471,765	869,976	1,005,748
All other revenues
Segment Reporting Information [Line Items]
Total revenues	$ 38,045	$ 40,685	$ 72,244	$ 74,278