Premises and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment
Depreciation	$ 38.8	$ 34.3	$ 35.1
Premises and equipment, gross	673.1	673.5
Less accumulated depreciation	(245.9)	(229.2)
Premises and equipment, net	427.2	444.3
Land
Property, Plant and Equipment
Premises and equipment, gross	87.2	87.7
Buildings and improvements
Property, Plant and Equipment
Premises and equipment, gross	473.7	474.2
Furniture and equipment
Property, Plant and Equipment
Premises and equipment, gross	$ 112.2	$ 111.6