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Investment Securities - Credit Quality Indicators (Details) - USD ($) $ in Millions | Jun. 30, 2023 | Dec. 31, 2022
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Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | $ 3,318.4 | $ 3,453.7
AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 3,149.9 | 3,260.7
AA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 92.6 | 92.8
A |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 10.6 | 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 | 13.2 | 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 | 397.8 | 396.6
U.S. Treasury notes | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 397.8 | 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 | 180.5 | 181.2
State, county, and municipal securities | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 69.1 | 68.3
State, county, and municipal securities | AA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 92.6 | 92.8
State, county, and municipal securities | A |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 10.6 | 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 | 8.2 | 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 | 353.1 | 351.7
Obligations of U.S. government agencies | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 353.1 | 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
Commercial Mortgage-Backed Securities |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 517.8 | 526.8
Commercial Mortgage-Backed Securities | FNMA/FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 361.9 | 364.9
Commercial Mortgage-Backed Securities | FNMA/FHLMC | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 361.9 | 364.9
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 | 155.9 | 161.9
Commercial Mortgage-Backed Securities | GNMA | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 155.9 | 161.9
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 | 1,311.4 | 1,391.5
Residential Mortgage Backed Securities | FNMA/FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 1,265.8 | 1,342.9
Residential Mortgage Backed Securities | FNMA/FHLMC | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 1,265.8 | 1,342.9
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 | 45.6 | 48.6
Residential Mortgage Backed Securities | GNMA | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 45.6 | 48.6
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 | 500.7 | 525.8
Collateralized Mortgage Obligations | FNMA/FHLMC |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 352.2 | 525.8
Collateralized Mortgage Obligations | FNMA/FHLMC | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 352.2 | 525.8
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 | 148.5 |
Collateralized Mortgage Obligations | GNMA | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 148.5 |
Collateralized Mortgage Obligations | GNMA | AA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 |
Collateralized Mortgage Obligations | GNMA | A |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 0.0 |
Collateralized Mortgage Obligations | GNMA | BBB |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | 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 |
Collateralized Mortgage Obligations | GNMA | BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity | $ 0.0 |
Other Security Investments |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity |  | 0.0
Other Security Investments | AAA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity |  | 0.0
Other Security Investments | AA |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity |  | 0.0
Other Security Investments | A |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity |  | 0.0
Other Security Investments | BBB |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity |  | 0.0
Other Security Investments | Not Rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity |  | 0.0
Other Security Investments | BB Rating |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Investment securities classified as held to maturity |  | $ 0.0

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