Quarterly report [Sections 13 or 15(d)]

Mergers and Acquisitions - Narrative (Details)

v3.25.1
Mergers and Acquisitions - Narrative (Details)
$ in Millions
 3 Months Ended 12 Months Ended
Feb. 03, 2025
USD ($)
Nov. 04, 2024
USD ($)
managingGeneralUnderwriter
Oct. 01, 2024
USD ($)
Sep. 13, 2024
USD ($)
program
Sep. 01, 2024
USD ($)
Aug. 30, 2024
USD ($)
May 01, 2024
USD ($)
Mar. 31, 2025
USD ($)
Mar. 31, 2024
USD ($)
Dec. 31, 2024
USD ($)
Business Acquisition [Line Items]                    
Incremental amortization expense on intangible assets acquired                 $ 34.0  
Increase (decrease) of income tax expense related to the common control reorganization               $ (48.1) 59.6  
Increase in financing costs and interest expense                 48.4  
Increase (decrease) in transaction costs               (5.3) 10.7  
Decrease in tax expenses related to pro forma adjustments                 $ 12.8  
Contingent consideration obligation, maximum               532.5    
Contingently returnable consideration, maximum               12.9    
Velocity Risk Underwriters, LLC                    
Business Acquisition [Line Items]                    
Cash consideration for acquisition $ 548.6                  
Contingent consideration liabilities $ 21.1                  
Acquisition related costs               $ 3.9    
Castel Underwriting Agencies Limited                    
Business Acquisition [Line Items]                    
Cash consideration for acquisition             $ 247.6      
Measurement period adjustments, deferred tax liabilities                   $ 1.6
Measurement period adjustments, taxes payable                   0.9
Measurement period adjustments, working capital                   0.5
Measurement period adjustments increase (decrease), goodwill                   (2.0)
Contingently returnable consideration             4.9      
Castel Underwriting Agencies Limited | Class A Common Stock                    
Business Acquisition [Line Items]                    
Equity consideration for acquisition             $ 2.2      
US Assure Insurance Services of Florida, Inc.                    
Business Acquisition [Line Items]                    
Cash consideration for acquisition           $ 1,079.8        
Contingent consideration liabilities           $ 103.8        
Measurement period adjustments increase (decrease), goodwill                   5.2
Greenhill Underwriting Insurance Services, LLC                    
Business Acquisition [Line Items]                    
Cash consideration for acquisition         $ 11.7          
Measurement period adjustments, working capital                   0.4
Measurement period adjustments increase (decrease), goodwill                   0.3
Measurement period adjustments, intangibles                   $ 0.1
Ethos Property And Casualty Managing General Underwriters                    
Business Acquisition [Line Items]                    
Cash consideration for acquisition       $ 44.0            
Underwriting programs for insurance carriers (in programs) | program       8            
EverSports & Entertainment Insurance, Inc                    
Business Acquisition [Line Items]                    
Cash consideration for acquisition     $ 43.1              
Innovisk Capital Partners                    
Business Acquisition [Line Items]                    
Cash consideration for acquisition   $ 426.8                
Number of managing general underwriters | managingGeneralUnderwriter   7