Premises and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment
Depreciation	$ 28.0	$ 25.8	$ 23.3
Premises and equipment, gross	495.8	491.3
Less accumulated depreciation	(196.2)	(179.0)
Premises and equipment, net	299.6	312.3
Land
Property, Plant and Equipment
Premises and equipment, gross	52.0	52.9
Buildings and improvements
Property, Plant and Equipment
Premises and equipment, gross	346.8	349.5
Furniture and equipment
Property, Plant and Equipment
Premises and equipment, gross	$ 97.0	$ 88.9

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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