Derivatives and Hedging Activities - Offsetting Assets and Liabilities (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Financial Assets
Gross Amounts Recognized	$ 28.6		$ 28.6		$ 37.4
Gross Amounts Offset in the Balance Sheet	0.0		0.0		0.0
Net Amounts in the Balance Sheet	28.6		28.6		37.4
Financial Instruments	0.0		0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	25.8		25.8		32.7
Net Amount	2.8		2.8		4.7
Financial Liabilities
Gross Amounts Recognized	94.2		94.2		127.3
Gross Amounts Offset in the Balance Sheet	0.0		0.0		0.0
Net Amounts in the Balance Sheet	94.2		94.2		127.3
Financial Instruments	0.0		0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	0.0		0.0		0.0
Net Amount	94.2		94.2		127.3
Repurchase agreements
Gross Amounts Recognized	557.2		557.2		782.7
Gross Amounts Offset in the Balance Sheet	0.0		0.0		0.0
Net Amounts in the Balance Sheet	557.2		557.2		782.7
Financial Instruments	0.0		0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	0.0		0.0		0.0
Net Amount	557.2		557.2		782.7
Total assets and liabilities
Gross Amounts Recognized	651.4		651.4		910.0
Gross Amounts Offset in the Balance Sheet	0.0		0.0		0.0
Net Amounts in the Balance Sheet	651.4		651.4		910.0
Financial Instruments	0.0		0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	0.0		0.0		0.0
Net Amount	651.4		651.4		910.0
Derivative Liability, Notional Amount	1,868.9		1,868.9		2,295.7
Not Designated as Hedging Instrument
Total assets and liabilities
Amount of net gains recognized in mortgage banking revenues	0.0	$ 0.1	0.0	$ (0.1)
Interest Rate Swap
Financial Assets
Gross Amounts Recognized	28.6		28.6		37.3
Gross Amounts Offset in the Balance Sheet	0.0		0.0		0.0
Net Amounts in the Balance Sheet	28.6		28.6		37.3
Financial Instruments	0.0		0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	25.8		25.8		32.7
Net Amount	2.8		2.8		4.6
Interest Rate Swap | Not Designated as Hedging Instrument
Total assets and liabilities
Derivative Liability, Notional Amount	1,468.5		1,468.5		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	95.5		95.5		101.1
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	94.2		94.2		127.1
Gross Amounts Offset in the Balance Sheet	0.0		0.0		0.0
Net Amounts in the Balance Sheet	94.2		94.2		127.1
Financial Instruments	0.0		0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	0.0		0.0		0.0
Net Amount	94.2		94.2		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	$ 4.9		$ 4.9		$ 5.6