Goodwill and Core Deposit Intangibles - Schedule of Finite-Lived Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2023	Dec. 31, 2021
Finite-lived Intangible Assets [Roll Forward]
Finite-Lived Intangible Assets, Gross	$ 177.5		$ 106.0
Finite-lived intangible assets acquired	72.9
Finite-Lived Intangible Assets, Period Increase (Decrease)	(1.4)
Finite-Lived Intangible Assets, Accumulated Amortization	(80.5)	$ (96.1)
Finite-Lived Intangible Assets, Net	97.0	81.4
Core Deposits Intangibles
Finite-lived Intangible Assets [Roll Forward]
Finite-Lived Intangible Assets, Gross	154.7		106.0
Finite-lived intangible assets acquired	50.1
Finite-Lived Intangible Assets, Period Increase (Decrease)	(1.4)
Finite-Lived Intangible Assets, Accumulated Amortization	(78.8)	(92.5)
Finite-Lived Intangible Assets, Net	75.9	62.2
OCRI
Finite-lived Intangible Assets [Roll Forward]
Finite-Lived Intangible Assets, Gross	22.8		$ 0.0
Finite-lived intangible assets acquired	22.8
Finite-Lived Intangible Assets, Period Increase (Decrease)	0.0
Finite-Lived Intangible Assets, Accumulated Amortization	(1.7)	(3.6)
Finite-Lived Intangible Assets, Net	$ 21.1	$ 19.2