Quarterly report [Sections 13 or 15(d)]

Mergers and Acquisitions - Narrative (Details)

v3.26.1
Mergers and Acquisitions - Narrative (Details) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Dec. 01, 2025
Jul. 01, 2025
May 16, 2025
May 01, 2025
Feb. 03, 2025
Mar. 31, 2026
Mar. 31, 2025
Dec. 31, 2025
Business Combination [Line Items]                
Acquisition related costs             $ 3.9  
Velocity Risk Underwriters, LLC                
Business Combination [Line Items]                
Cash consideration         $ 549.6      
Contingent consideration liabilities         $ 19.6      
Measurement period adjustment, contingent consideration               $ 1.5
Measurement period adjustment, other current assets               1.5
Measurement period adjustments, working capital               0.9
Measurement period adjustments increase (decrease), goodwill               0.9
USQRisk Holdings, LLC                
Business Combination [Line Items]                
Cash consideration       $ 28.9        
Contingent consideration liabilities       $ 23.8        
Measurement period adjustments increase (decrease), goodwill               0.2
360° Underwriting                
Business Combination [Line Items]                
Cash consideration     $ 28.2          
Contingent consideration liabilities     $ 0.6          
J.M. Wilson Corporation                
Business Combination [Line Items]                
Cash consideration   $ 67.2            
Measurement period adjustments, working capital               0.6
Measurement period adjustments increase (decrease), goodwill               0.6
Equity consideration for acquisition   $ 20.4            
Measurement period adjustment related to commissions and fees receivable – net               0.8
Measurement period adjustments, intangibles               $ 0.4
Stewart Specialty Risk Underwriting Ltd.                
Business Combination [Line Items]                
Cash consideration $ 124.3              
Measurement period adjustments increase (decrease), goodwill           $ 1.3    
Stewart Specialty Risk Underwriting Ltd. | Class A Common Stock                
Business Combination [Line Items]                
Equity consideration for acquisition $ 8.1              
Business Combinations, Aggregate Business Combinations                
Business Combination [Line Items]                
Contingent consideration obligation, maximum           597.3    
Contingently returnable consideration, maximum           $ 6.6