Quarterly report pursuant to Section 13 or 15(d)

Revenue from Contracts with Customers - Summary of Revenue from Contracts (Detail)

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Revenue from Contracts with Customers - Summary of Revenue from Contracts (Detail) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2022
Mar. 31, 2021
Disaggregation of Revenue [Line Items]    
Net commissions and fees $ 386,681 $ 311,344
Wholesale brokerage [Member]    
Disaggregation of Revenue [Line Items]    
Net commissions and fees 244,827 191,124
Binding authorities [Member]    
Disaggregation of Revenue [Line Items]    
Net commissions and fees 62,993 55,045
Underwriting management [Member]    
Disaggregation of Revenue [Line Items]    
Net commissions and fees $ 78,861 $ 65,175