Derivatives and Hedging Activities - Offsetting Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Financial Assets
Gross Amounts Recognized	$ 27.1	$ 26.6
Gross Amounts Offset in the Balance Sheet	0.0	0.0
Net Amounts in the Balance Sheet	27.1	26.6
Financial Instruments	0.0	0.0
Fair Value of Financial Collateral in the Balance Sheet	27.0	26.4
Net Amount	0.1	0.2
Financial Liabilities
Gross Amounts Recognized	76.8	77.3
Gross Amounts Offset in the Balance Sheet	0.0	0.0
Net Amounts in the Balance Sheet	76.8	77.3
Financial Instruments	0.0	0.0
Fair Value of Financial Collateral in the Balance Sheet	0.0	0.0
Net Amount	76.8	77.3
Repurchase agreements
Gross Amounts Recognized	476.1	479.6
Gross Amounts Offset in the Balance Sheet	0.0	0.0
Net Amounts in the Balance Sheet	476.1	479.6
Financial Instruments	0.0	0.0
Fair Value of Financial Collateral in the Balance Sheet	0.0	0.0
Net Amount	476.1	479.6
Total assets and liabilities
Gross Amounts Recognized	552.9	556.9
Gross Amounts Offset in the Balance Sheet	0.0	0.0
Net Amounts in the Balance Sheet	552.9	556.9
Financial Instruments	0.0	0.0
Fair Value of Financial Collateral in the Balance Sheet	0.0	0.0
Net Amount	552.9	556.9
Derivative Liability, Notional Amount	1,189.3	1,269.5
Interest Rate Swap | Not Designated as Hedging Instrument
Total assets and liabilities
Derivative Liability, Notional Amount	1,126.0	1,204.9
Risk Participation Agreements | Not Designated as Hedging Instrument
Total assets and liabilities
Derivative Liability, Notional Amount	63.3	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	27.0	26.6
Gross Amounts Offset in the Balance Sheet	0.0	0.0
Net Amounts in the Balance Sheet	27.0	26.6
Financial Instruments	0.0	0.0
Fair Value of Financial Collateral in the Balance Sheet	27.0	26.4
Net Amount	0.0	0.2
Financial Liabilities
Gross Amounts Recognized	76.8	77.3
Gross Amounts Offset in the Balance Sheet	0.0	0.0
Net Amounts in the Balance Sheet	76.8	77.3
Financial Instruments	0.0	0.0
Fair Value of Financial Collateral in the Balance Sheet	0.0	0.0
Net Amount	$ 76.8	$ 77.3