Goodwill and Core Deposit Intangibles - Schedule of Core Deposit Intangibles Activity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Finite-lived Intangible Assets [Roll Forward]
Accumulated amortization	$ 9.9	$ 10.9	$ 11.2
Finite-Lived Intangible Asset, Useful Life	10 years
Core Deposits Intangibles
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross		106.0	$ 106.0
Finite-lived Intangible Assets [Roll Forward]
Gross CDI, beginning of period	$ 51.2
Finite-Lived Intangible Assets, Accumulated Amortization	64.7	54.8
Net CDI, end of period	$ 41.3	$ 51.2