Investment Securities - Credit Quality Indicators (Details) - USD ($) $ in Millions	Jun. 30, 2026	Dec. 31, 2025
Schedule of Held-to-maturity Securities [Line Items]
Investment securities classified as held to maturity	$ 2,215.9	$ 2,342.6
State, county, and municipal securities
Schedule of Held-to-maturity Securities [Line Items]
Investment securities classified as held to maturity	164.9	173.2
Obligations of U.S. government agencies
Schedule of Held-to-maturity Securities [Line Items]
Investment securities classified as held to maturity	455.9	462.3
Corporate securities
Schedule of Held-to-maturity Securities [Line Items]
Investment securities classified as held to maturity	10.9	29.9
Commercial Mortgage-Backed Securities
Schedule of Held-to-maturity Securities [Line Items]
Investment securities classified as held to maturity	351.8	354.8
Residential Mortgage Backed Securities
Schedule of Held-to-maturity Securities [Line Items]
Investment securities classified as held to maturity	873.9	941.3
Collateralized Mortgage Obligations
Schedule of Held-to-maturity Securities [Line Items]
Investment securities classified as held to maturity	$ 358.5	$ 381.1