Goodwill and Core Deposit Intangibles - Schedule of Finite-Lived Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Finite-lived Intangible Assets [Roll Forward]
Finite-Lived Intangible Assets, Gross		$ 177.5	$ 177.5
Finite-Lived Intangible Assets, Accumulated Amortization	$ (124.2)	(110.7)
Finite-Lived Intangible Assets, Net	53.3	66.8
Core Deposits Intangibles
Finite-lived Intangible Assets [Roll Forward]
Finite-Lived Intangible Assets, Gross		154.7	154.7
Finite-Lived Intangible Assets, Accumulated Amortization	(116.9)	(105.2)
Finite-Lived Intangible Assets, Net	37.8	49.5
OCRI
Finite-lived Intangible Assets [Roll Forward]
Finite-Lived Intangible Assets, Gross		22.8	$ 22.8
Finite-Lived Intangible Assets, Accumulated Amortization	(7.3)	(5.5)
Finite-Lived Intangible Assets, Net	$ 15.5	$ 17.3