v3.25.1
Disclosures About Fair Value of Financial Instruments - Schedule of Company's Financial Instruments Whose Carrying Amount Did Not Equal Fair Value (Details) - USD ($)
$ in Millions
Mar. 31, 2025
Dec. 31, 2024
Carrying Amount    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial instruments $ 372.7 $ 372.0
Fair Value    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial instruments 363.2 373.8
Junior subordinated debentures | Carrying Amount    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial instruments 243.7 243.2
Junior subordinated debentures | Fair Value    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial instruments 244.1 245.2
Junior subordinated debentures | Trust preferred debentures | Carrying Amount    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial instruments 162.3 162.0
Junior subordinated debentures | Trust preferred debentures | Fair Value    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial instruments 162.8 163.9
Junior subordinated debentures | Subordinated debentures | Carrying Amount    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial instruments 81.4 81.2
Junior subordinated debentures | Subordinated debentures | Fair Value    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial instruments 81.3 81.3
Senior unsecured fixed rate notes | Carrying Amount    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial instruments 129.0 128.8
Senior unsecured fixed rate notes | Fair Value    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Financial instruments $ 119.1 $ 128.6