Quarterly report pursuant to Section 13 or 15(d)

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

v3.21.2
Revenue from Contracts with Customers - Summary of Revenue from Contracts (Detail) - 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]        
Net commissions and fees $ 352,610 $ 236,683 $ 1,053,800 $ 689,833
Wholesale brokerage [Member]        
Disaggregation of Revenue [Line Items]        
Net commissions and fees 229,146 154,484 676,229 460,706
Binding authorities [Member]        
Disaggregation of Revenue [Line Items]        
Net commissions and fees 52,795 36,130 161,436 101,837
Underwriting management [Member]        
Disaggregation of Revenue [Line Items]        
Net commissions and fees $ 70,669 $ 46,069 $ 216,135 $ 127,290