Derivatives and Hedging Activities - Offsetting Assets and Liabilities (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Financial Assets
Gross Amounts Recognized	$ 45.0		$ 45.0		$ 37.4
Gross Amounts Offset in the Balance Sheet	0.0		0.0		0.0
Net Amounts in the Balance Sheet	45.0		45.0		37.4
Financial Instruments	0.0		0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	31.5		31.5		32.7
Net Amount	13.5		13.5		4.7
Financial Liabilities
Gross Amounts Recognized	157.2		157.2		127.3
Gross Amounts Offset in the Balance Sheet	0.0		0.0		0.0
Net Amounts in the Balance Sheet	157.2		157.2		127.3
Financial Instruments	0.0		0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	2.0		2.0		0.0
Net Amount	155.2		155.2		127.3
Repurchase agreements
Gross Amounts Recognized	741.8		741.8		782.7
Gross Amounts Offset in the Balance Sheet	0.0		0.0		0.0
Net Amounts in the Balance Sheet	741.8		741.8		782.7
Financial Instruments	0.0		0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	741.8		741.8		782.7
Net Amount	0.0		0.0		0.0
Total assets and liabilities
Gross Amounts Recognized	899.0		899.0		910.0
Gross Amounts Offset in the Balance Sheet	0.0		0.0		0.0
Net Amounts in the Balance Sheet	899.0		899.0		910.0
Financial Instruments	0.0		0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	743.8		743.8		782.7
Net Amount	155.2		155.2		127.3
Derivative Liability, Notional Amount	2,757.0		2,757.0		2,295.7
Not Designated as Hedging Instrument
Total assets and liabilities
Amount of net gains recognized in mortgage banking revenues	0.0	$ (0.2)	0.0	$ (0.2)
Interest Rate Swap
Financial Assets
Gross Amounts Recognized	45.0		45.0		37.3
Gross Amounts Offset in the Balance Sheet	0.0		0.0		0.0
Net Amounts in the Balance Sheet	45.0		45.0		37.3
Financial Instruments	0.0		0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	31.5		31.5		32.7
Net Amount	13.5		13.5		4.6
Interest Rate Swap | Not Designated as Hedging Instrument
Total assets and liabilities
Derivative Liability, Notional Amount	1,500.0		1,500.0		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	98.5		98.5		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	157.2		157.2		127.1
Gross Amounts Offset in the Balance Sheet	0.0		0.0		0.0
Net Amounts in the Balance Sheet	157.2		157.2		127.1
Financial Instruments	0.0		0.0		0.0
Fair Value of Financial Collateral in the Balance Sheet	2.0		2.0		0.0
Net Amount	155.2		155.2		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	$ 8.5		$ 8.5		$ 5.6