Investment Securities - Credit Quality Indicators (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Schedule of Held-to-maturity Securities [Line Items]
Investment securities classified as held to maturity	$ 2,640.3	$ 2,688.4
U.S. Treasury notes
Schedule of Held-to-maturity Securities [Line Items]
Investment securities classified as held to maturity	99.8	99.8
State, county, and municipal securities
Schedule of Held-to-maturity Securities [Line Items]
Investment securities classified as held to maturity	176.2	176.3
Obligations of U.S. government agencies
Schedule of Held-to-maturity Securities [Line Items]
Investment securities classified as held to maturity	468.2	470.1
Corporate securities
Schedule of Held-to-maturity Securities [Line Items]
Investment securities classified as held to maturity	56.9	57.0
Commercial Mortgage-Backed Securities
Schedule of Held-to-maturity Securities [Line Items]
Investment securities classified as held to maturity	372.7	374.9
Residential Mortgage Backed Securities
Schedule of Held-to-maturity Securities [Line Items]
Investment securities classified as held to maturity	1,049.2	1,082.5
Collateralized Mortgage Obligations
Schedule of Held-to-maturity Securities [Line Items]
Investment securities classified as held to maturity	$ 417.3	$ 427.8