Goodwill and Core Deposit Intangibles - Schedule of Finite-Lived Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Finite-lived Intangible Assets [Roll Forward]
Finite-Lived Intangible Assets, Gross		$ 177.5	$ 177.5
Finite-Lived Intangible Assets, Accumulated Amortization	$ (110.7)	(96.1)
Finite-Lived Intangible Assets, Net	66.8	81.4
Core Deposits Intangibles
Finite-lived Intangible Assets [Roll Forward]
Finite-Lived Intangible Assets, Gross		154.7	154.7
Finite-Lived Intangible Assets, Accumulated Amortization	(105.2)	(92.5)
Finite-Lived Intangible Assets, Net	49.5	62.2
OCRI
Finite-lived Intangible Assets [Roll Forward]
Finite-Lived Intangible Assets, Gross		22.8	$ 22.8
Finite-Lived Intangible Assets, Accumulated Amortization	(5.5)	(3.6)
Finite-Lived Intangible Assets, Net	$ 17.3	$ 19.2