Segment, Geographic and Product Information - Product Information Regarding Revenues (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Segment Reporting Information [Line Items]
Total revenues	$ 416,567	$ 473,747	$ 1,358,787	$ 1,553,773
Rates
Segment Reporting Information [Line Items]
Total revenues	129,971	128,508	425,909	426,775
FX
Segment Reporting Information [Line Items]
Total revenues	73,481	72,976	227,853	229,216
Energy and commodities
Segment Reporting Information [Line Items]
Total revenues	68,975	74,328	218,057	224,931
Credit
Segment Reporting Information [Line Items]
Total revenues	58,187	58,983	203,352	221,639
Equities
Segment Reporting Information [Line Items]
Total revenues	48,384	54,715	173,803	186,002
Insurance
Segment Reporting Information [Line Items]
Total revenues	0	51,503	0	158,198
Total brokerage revenues
Segment Reporting Information [Line Items]
Total revenues	378,998	441,013	1,248,974	1,446,761
All other revenues
Segment Reporting Information [Line Items]
Total revenues	$ 37,569	$ 32,734	$ 109,813	$ 107,012