Derivatives and Hedging Activities - Offsetting Assets and Liabilities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Financial Assets
Gross Amounts Recognized	$ 44.2		$ 37.4
Gross Amounts Offset in the Balance Sheet	0.0		0.0
Net Amounts in the Balance Sheet	44.2		37.4
Financial Instruments	0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	32.5		32.7
Net Amount	11.7		4.7
Financial Liabilities
Gross Amounts Recognized	156.6		127.3
Gross Amounts Offset in the Balance Sheet	0.0		0.0
Net Amounts in the Balance Sheet	156.6		127.3
Financial Instruments	0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	0.0		0.0
Net Amount	156.6		127.3
Repurchase agreements
Gross Amounts Recognized	794.2		782.7
Gross Amounts Offset in the Balance Sheet	0.0		0.0
Net Amounts in the Balance Sheet	794.2		782.7
Financial Instruments	0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	794.2		782.7
Net Amount	0.0		0.0
Total assets and liabilities
Gross Amounts Recognized	950.8		910.0
Gross Amounts Offset in the Balance Sheet	0.0		0.0
Net Amounts in the Balance Sheet	950.8		910.0
Financial Instruments	0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	794.2		782.7
Net Amount	156.6		127.3
Derivative Liability, Notional Amount	2,793.9		2,295.7
Not Designated as Hedging Instrument
Total assets and liabilities
Amount of net gains recognized in mortgage banking revenues	0.1	$ 0.1
Interest Rate Swap
Financial Assets
Gross Amounts Recognized	44.1		37.3
Gross Amounts Offset in the Balance Sheet	0.0		0.0
Net Amounts in the Balance Sheet	44.1		37.3
Financial Instruments	0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	32.5		32.7
Net Amount	11.6		4.6
Interest Rate Swap | Not Designated as Hedging Instrument
Total assets and liabilities
Derivative Liability, Notional Amount	1,535.6		1,589.0
Risk Participation Agreements
Financial Liabilities
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
Risk Participation Agreements | Not Designated as Hedging Instrument
Total assets and liabilities
Derivative Liability, Notional Amount	99.7		101.1
Interest Rate Lock Commitments
Financial Assets
Gross Amounts Recognized	0.1		0.1
Gross Amounts Offset in the Balance Sheet	0.0		0.0
Net Amounts in the Balance Sheet	0.1		0.1
Financial Instruments	0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	0.0		0.0
Net Amount	0.1		0.1
Interest Rate Lock Commitments | Not Designated as Hedging Instrument
Total assets and liabilities
Derivative Liability, Notional Amount	0.0		0.0
Interest Rate Swap and Interest Rate Collar
Financial Liabilities
Gross Amounts Recognized	156.6		127.1
Gross Amounts Offset in the Balance Sheet	0.0		0.0
Net Amounts in the Balance Sheet	156.6		127.1
Financial Instruments	0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	0.0		0.0
Net Amount	156.6		127.1
Forward Contracts
Financial Liabilities
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
Forward Contracts | Not Designated as Hedging Instrument
Total assets and liabilities
Derivative Liability, Notional Amount	$ 8.6		$ 5.6