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Investment Securities - Credit Quality Indicators (Details) - USD ($) $ in Millions | Sep. 30, 2024 | Dec. 31, 2023
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Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | $ 2,742.0 | $ 3,208.7
AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 2,594.0 | 3,041.5
AA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 74.2 | 92.3
A |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 10.1 | 10.6
BBB |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 47.0 | 47.0
Not Rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 11.7 | 12.3
BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 5.0 | 5.0
U.S. Treasury notes |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 99.6 | 399.0
U.S. Treasury notes | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 99.6 | 399.0
U.S. Treasury notes | AA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
U.S. Treasury notes | A |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
U.S. Treasury notes | BBB |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
U.S. Treasury notes | Not Rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
U.S. Treasury notes | BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
State, county, and municipal securities |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 176.7 | 179.2
State, county, and municipal securities | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 85.7 | 69.0
State, county, and municipal securities | AA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 74.2 | 92.3
State, county, and municipal securities | A |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 10.1 | 10.6
State, county, and municipal securities | BBB |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
State, county, and municipal securities | Not Rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 6.7 | 7.3
State, county, and municipal securities | BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Obligations of U.S. government agencies |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 356.4 | 354.5
Obligations of U.S. government agencies | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 356.4 | 354.5
Obligations of U.S. government agencies | AA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Obligations of U.S. government agencies | A |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Obligations of U.S. government agencies | BBB |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Obligations of U.S. government agencies | Not Rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Obligations of U.S. government agencies | BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Corporate securities |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 57.0 | 57.0
Corporate securities | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Corporate securities | AA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Corporate securities | A |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Corporate securities | BBB |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 47.0 | 47.0
Corporate securities | Not Rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 5.0 | 5.0
Corporate securities | BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 5.0 | 5.0
Commercial Mortgage-Backed Securities |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 493.0 | 510.5
Commercial Mortgage-Backed Securities | FNMA/FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 349.7 | 359.7
Commercial Mortgage-Backed Securities | FNMA/FHLMC | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 349.7 | 359.7
Commercial Mortgage-Backed Securities | FNMA/FHLMC | AA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Commercial Mortgage-Backed Securities | FNMA/FHLMC | A |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Commercial Mortgage-Backed Securities | FNMA/FHLMC | BBB |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Commercial Mortgage-Backed Securities | FNMA/FHLMC | Not Rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Commercial Mortgage-Backed Securities | FNMA/FHLMC | BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Commercial Mortgage-Backed Securities | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 143.3 | 150.8
Commercial Mortgage-Backed Securities | GNMA | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 143.3 | 150.8
Commercial Mortgage-Backed Securities | GNMA | AA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Commercial Mortgage-Backed Securities | GNMA | A |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Commercial Mortgage-Backed Securities | GNMA | BBB |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Commercial Mortgage-Backed Securities | GNMA | Not Rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Commercial Mortgage-Backed Securities | GNMA | BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Residential Mortgage Backed Securities |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 1,119.5 | 1,232.6
Residential Mortgage Backed Securities | FNMA/FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 1,080.7 | 1,189.8
Residential Mortgage Backed Securities | FNMA/FHLMC | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 1,080.7 | 1,189.8
Residential Mortgage Backed Securities | FNMA/FHLMC | AA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Residential Mortgage Backed Securities | FNMA/FHLMC | A |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Residential Mortgage Backed Securities | FNMA/FHLMC | BBB |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Residential Mortgage Backed Securities | FNMA/FHLMC | Not Rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Residential Mortgage Backed Securities | FNMA/FHLMC | BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Residential Mortgage Backed Securities | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 38.8 | 42.8
Residential Mortgage Backed Securities | GNMA | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 38.8 | 42.8
Residential Mortgage Backed Securities | GNMA | AA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Residential Mortgage Backed Securities | GNMA | A |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Residential Mortgage Backed Securities | GNMA | BBB |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Residential Mortgage Backed Securities | GNMA | Not Rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Residential Mortgage Backed Securities | GNMA | BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Collateralized Mortgage Obligations |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 439.8 | 475.9
Collateralized Mortgage Obligations | FNMA/FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 308.5 | 334.1
Collateralized Mortgage Obligations | FNMA/FHLMC | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 308.5 | 334.1
Collateralized Mortgage Obligations | FNMA/FHLMC | AA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Collateralized Mortgage Obligations | FNMA/FHLMC | A |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Collateralized Mortgage Obligations | FNMA/FHLMC | BBB |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Collateralized Mortgage Obligations | FNMA/FHLMC | Not Rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Collateralized Mortgage Obligations | FNMA/FHLMC | BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Collateralized Mortgage Obligations | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 131.3 | 141.8
Collateralized Mortgage Obligations | GNMA | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 131.3 | 141.8
Collateralized Mortgage Obligations | GNMA | AA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Collateralized Mortgage Obligations | GNMA | A |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Collateralized Mortgage Obligations | GNMA | BBB |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Collateralized Mortgage Obligations | GNMA | Not Rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
Collateralized Mortgage Obligations | GNMA | BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | $ 0.0 | $ 0.0

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