Quarterly report pursuant to Section 13 or 15(d)

Mergers and Acquisitions - Additional Information (Detail)

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Mergers and Acquisitions - Additional Information (Detail) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
May 01, 2024
Dec. 01, 2023
Jul. 03, 2023
Jul. 01, 2023
Jan. 03, 2023
Jun. 30, 2024
Jun. 30, 2023
Jun. 30, 2024
Jun. 30, 2023
Business Acquisition, Contingent Consideration [Line Items]                  
Business combinations - net of cash acquired and cash held in a fiduciary capacity               $ 214,093 $ 103,927
Contingent consideration           $ 1,243 $ 1,796 1,178 2,510
Contingently returnable consideration maximum           19,000   19,000  
Incremental amortization expense on intangible assets acquired           2,800 6,100 5,700 12,100
Increase in transaction costs           3,300   6,500 $ 5,700
Increase in income tax expense             $ 18,400    
Maximum contingent consideration obligation           98,100   $ 98,100  
Common Class A [Member]                  
Business Acquisition, Contingent Consideration [Line Items]                  
Consideration     $ 2,700            
Griffin [Member]                  
Business Acquisition, Contingent Consideration [Line Items]                  
Business combinations - net of cash acquired and cash held in a fiduciary capacity         $ 115,500        
Castel underwriting agencies ltd acquisition                  
Business Acquisition, Contingent Consideration [Line Items]                  
Business combinations - net of cash acquired and cash held in a fiduciary capacity $ 247,600                
Contingently returnable consideration 4,900                
Castel underwriting agencies ltd acquisition | Customer relationships [Member]                  
Business Acquisition, Contingent Consideration [Line Items]                  
Weighted average amortization period (in years)               13 years 2 months 12 days  
Castel underwriting agencies ltd acquisition | General and Administrative Expense [Member]                  
Business Acquisition, Contingent Consideration [Line Items]                  
Business combination, acquisition related costs           $ 1,200   $ 1,600  
Castel underwriting agencies ltd acquisition | Common Class A [Member]                  
Business Acquisition, Contingent Consideration [Line Items]                  
Consideration $ 2,200                
ACE Benefit Partners & Point6 Healthcare [Member]                  
Business Acquisition, Contingent Consideration [Line Items]                  
Business combinations - net of cash acquired and cash held in a fiduciary capacity       $ 46,800          
Contingent consideration       $ 2,300          
Measurement period adjustment to goodwill               600  
Socius Insurance Services Inc [Member]                  
Business Acquisition, Contingent Consideration [Line Items]                  
Business combinations - net of cash acquired and cash held in a fiduciary capacity     253,500            
Contingent consideration     $ 5,800            
AccuRisk Holdings [Member]                  
Business Acquisition, Contingent Consideration [Line Items]                  
Business combinations - net of cash acquired and cash held in a fiduciary capacity   $ 98,300              
Measurement period adjustment to goodwill               $ 300