v3.25.1
Disclosures About Fair Value of Financial Instruments - Schedule of Fair Values Measured on Recurring Basis (Details) - Fair Value, Recurring - USD ($)
$ in Millions
Mar. 31, 2025
Dec. 31, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Financial instruments $ 363.2 $ 373.8
Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Financial instruments 119.1 128.6
Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Financial instruments 244.1 245.2
Level 3    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Financial instruments 0.0 0.0
Junior subordinated debentures    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Financial instruments 244.1 245.2
Junior subordinated debentures | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Financial instruments 0.0 0.0
Junior subordinated debentures | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Financial instruments 244.1 245.2
Junior subordinated debentures | Level 3    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Financial instruments 0.0 0.0
Senior unsecured fixed rate notes    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Financial instruments 119.1 128.6
Senior unsecured fixed rate notes | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Financial instruments 119.1 128.6
Senior unsecured fixed rate notes | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Financial instruments 0.0 0.0
Senior unsecured fixed rate notes | Level 3    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Financial instruments 0.0 0.0
Trust preferred debentures | Junior subordinated debentures    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Financial instruments 162.8 163.9
Trust preferred debentures | Junior subordinated debentures | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Financial instruments 0.0 0.0
Trust preferred debentures | Junior subordinated debentures | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Financial instruments 162.8 163.9
Trust preferred debentures | Junior subordinated debentures | Level 3    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Financial instruments 0.0 0.0
Subordinated debentures | Junior subordinated debentures    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Financial instruments 81.3 81.3
Subordinated debentures | Junior subordinated debentures | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Financial instruments 0.0 0.0
Subordinated debentures | Junior subordinated debentures | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Financial instruments 81.3 81.3
Subordinated debentures | Junior subordinated debentures | Level 3    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Financial instruments $ 0.0 $ 0.0