Derivatives and Hedging Activities - Offsetting Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Financial Assets
Gross Amounts Recognized	$ 35.3	$ 44.9
Gross Amounts Offset in the Balance Sheet	0.0	0.0
Net Amounts in the Balance Sheet	35.3	44.9
Financial Instruments	0.0	0.0
Fair Value of Financial Collateral in the Balance Sheet	35.3	42.4
Net Amount	0.0	2.5
Financial Liabilities
Gross Amounts Recognized	107.3	133.8
Gross Amounts Offset in the Balance Sheet	0.0	0.0
Net Amounts in the Balance Sheet	107.3	133.8
Financial Instruments	0.0	0.0
Fair Value of Financial Collateral in the Balance Sheet	0.0	0.0
Net Amount	107.3	133.8
Repurchase agreements
Gross Amounts Recognized	528.0	523.9
Gross Amounts Offset in the Balance Sheet	0.0	0.0
Net Amounts in the Balance Sheet	528.0	523.9
Financial Instruments	0.0	0.0
Fair Value of Financial Collateral in the Balance Sheet	0.0	0.0
Net Amount	528.0	523.9
Total assets and liabilities
Gross Amounts Recognized	635.3	657.7
Gross Amounts Offset in the Balance Sheet	0.0	0.0
Net Amounts in the Balance Sheet	635.3	657.7
Financial Instruments	0.0	0.0
Fair Value of Financial Collateral in the Balance Sheet	0.0	0.0
Net Amount	635.3	657.7
Derivative Liability, Notional Amount	2,086.4	2,107.0
Interest Rate Swap
Financial Assets
Gross Amounts Recognized	35.2	44.9
Gross Amounts Offset in the Balance Sheet	0.0	0.0
Net Amounts in the Balance Sheet	35.2	44.9
Financial Instruments	0.0	0.0
Fair Value of Financial Collateral in the Balance Sheet	35.3	42.4
Net Amount	(0.1)	2.5
Interest Rate Swap | Not Designated as Hedging Instrument
Total assets and liabilities
Derivative Liability, Notional Amount	1,390.7	1,415.4
Risk Participation Agreements | Not Designated as Hedging Instrument
Total assets and liabilities
Derivative Liability, Notional Amount	89.0	91.6
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 Liabilities
Gross Amounts Recognized	107.3	133.8
Gross Amounts Offset in the Balance Sheet	0.0	0.0
Net Amounts in the Balance Sheet	107.3	133.8
Financial Instruments	0.0	0.0
Fair Value of Financial Collateral in the Balance Sheet	0.0	0.0
Net Amount	107.3	133.8
Forward Contracts | Not Designated as Hedging Instrument
Total assets and liabilities
Derivative Liability, Notional Amount	$ 6.7	$ 0.0