Derivatives and Hedging Activities - Offsetting Assets and Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2026	Dec. 31, 2025
Financial Assets
Gross Amounts Recognized	$ 29.7	$ 26.6
Gross Amounts Offset in the Balance Sheet	0.0	0.0
Net Amounts in the Balance Sheet	29.7	26.6
Financial Instruments	0.0	0.0
Fair Value of Financial Collateral in the Balance Sheet	29.6	26.4
Net Amount	0.1	0.2
Financial Liabilities
Gross Amounts Recognized	81.2	77.3
Gross Amounts Offset in the Balance Sheet	0.0	0.0
Net Amounts in the Balance Sheet	81.2	77.3
Financial Instruments	0.0	0.0
Fair Value of Financial Collateral in the Balance Sheet	0.0	0.0
Net Amount	81.2	77.3
Repurchase agreements
Gross Amounts Recognized	455.2	479.6
Gross Amounts Offset in the Balance Sheet	0.0	0.0
Net Amounts in the Balance Sheet	455.2	479.6
Financial Instruments	0.0	0.0
Fair Value of Financial Collateral in the Balance Sheet	0.0	0.0
Net Amount	455.2	479.6
Total assets and liabilities
Gross Amounts Recognized	536.4	556.9
Gross Amounts Offset in the Balance Sheet	0.0	0.0
Net Amounts in the Balance Sheet	536.4	556.9
Financial Instruments	0.0	0.0
Fair Value of Financial Collateral in the Balance Sheet	0.0	0.0
Net Amount	536.4	556.9
Derivative Liability, Notional Amount	1,145.4	1,269.5
Interest Rate Swap | Not Designated as Hedging Instrument
Total assets and liabilities
Derivative Liability, Notional Amount	1,083.0	1,204.9
Risk Participation Agreements | Not Designated as Hedging Instrument
Total assets and liabilities
Derivative Liability, Notional Amount	62.4	64.6
Interest Rate Lock Commitments
Financial Assets
Gross Amounts Recognized	0.1
Gross Amounts Offset in the Balance Sheet	0.0
Net Amounts in the Balance Sheet	0.1
Financial Instruments	0.0
Fair Value of Financial Collateral in the Balance Sheet	0.0
Net Amount	0.1
Interest Rate Swap and Interest Rate Collar
Financial Assets
Gross Amounts Recognized	29.6	26.6
Gross Amounts Offset in the Balance Sheet	0.0	0.0
Net Amounts in the Balance Sheet	29.6	26.6
Financial Instruments	0.0	0.0
Fair Value of Financial Collateral in the Balance Sheet	29.6	26.4
Net Amount	0.0	0.2
Financial Liabilities
Gross Amounts Recognized	81.2	77.3
Gross Amounts Offset in the Balance Sheet	0.0	0.0
Net Amounts in the Balance Sheet	81.2	77.3
Financial Instruments	0.0	0.0
Fair Value of Financial Collateral in the Balance Sheet	0.0	0.0
Net Amount	$ 81.2	$ 77.3