Premises and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment
Depreciation	$ 25.8	$ 23.3	$ 16.2
Premises and equipment, gross	491.3	475.1
Less accumulated depreciation	(179.0)	(169.1)
Premises and equipment, net	312.3	306.0
Land
Property, Plant and Equipment
Premises and equipment, gross	52.9	50.8
Buildings and improvements
Property, Plant and Equipment
Premises and equipment, gross	349.5	330.1
Furniture and equipment
Property, Plant and Equipment
Premises and equipment, gross	$ 88.9	$ 94.2

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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The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

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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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