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Investment Securities - Credit Quality Indicators (Details) - USD ($) $ in Millions | Mar. 31, 2023 | Dec. 31, 2022
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Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | $ 3,376.9 | $ 3,453.7
AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 3,207.1 | 3,260.7
AA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 92.7 | 92.8
A |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 11.5 | 11.5
BBB |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 52.1 | 65.1
Not Rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 13.5 | 13.6
BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 10.0
U.S. Treasury notes |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 397.2 | 396.6
U.S. Treasury notes | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 397.2 | 396.6
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 | 180.9 | 181.2
State, county, and municipal securities | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 68.2 | 68.3
State, county, and municipal securities | AA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 92.7 | 92.8
State, county, and municipal securities | A |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 11.5 | 11.5
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 | 8.5 | 8.6
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 | 352.3 | 351.7
Obligations of U.S. government agencies | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 352.3 | 351.7
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 | 57.1 | 80.1
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 | 52.1 | 65.1
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 | 0.0 | 10.0
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 2,389.4 | 2,444.1
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations | FNMA/FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 2,183.2 | 2,233.6
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations | FNMA/FHLMC | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 2,183.2 | 2,233.6
U.S. agency residential & commercial mortgage-backed securities & 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
U.S. agency residential & commercial mortgage-backed securities & 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
U.S. agency residential & commercial mortgage-backed securities & 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
U.S. agency residential & commercial mortgage-backed securities & 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
U.S. agency residential & commercial mortgage-backed securities & 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
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations | GNMA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 206.2 | 210.5
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations | GNMA | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 206.2 | 210.5
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations | GNMA | AA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations | GNMA | A |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
U.S. agency residential & commercial mortgage-backed securities & collateralized mortgage obligations | GNMA | BBB |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 | 0.0
U.S. agency residential & commercial mortgage-backed securities & 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
U.S. agency residential & commercial mortgage-backed securities & 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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