Premises and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Land and Land Improvements	$ 32.4	$ 33.0
Furniture Fixtures And Equipment Gross	99.6	68.2
Leasehold Improvements, Gross	41.5	29.7
Construction in Progress, Gross	42.7	17.4
Property, Plant and Equipment, Gross	307.8	240.3
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(125.9)	(106.2)
Premises and equipment, net	181.9	134.1
Buildings and Improvements, Gross	91.6	92.0
Depreciation	$ 20.7	$ 15.2	$ 13.5
Operating Lease, Weighted Average Discount Rate, Percent	2.14%	2.80%	3.08%
Operating Lease, Weighted Average Remaining Lease Term	7 years 6 months	7 years 8 months 12 days	8 years 4 months 24 days
Lease, Cost	$ 18.8	$ 14.0	$ 12.9
Lessee, operating lease, other cost	$ 3.8	$ 3.9	$ 4.0