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Investment Securities - Narrative (Details) | Dec. 31, 2020 USD ($) instrument | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($)
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Schedule of Available for sale Securities and Held to maturity Securities [Line Items] |  |  |
Fair value of investments | $ 80,881,000 | $ 395,416,000 |
Unrealized losses on available for sale securities | 349,000 | 2,211,000 |
Unrealized losses in held to maturity portfolios | 252,000 | 545,000 |
Carrying value of securities pledged as collateral | 890,025,000 | 503,427,000 | $ 416,155,000
Securities sold under repurchase agreements | 167,265,000 | 182,856,000 |
Investments in Debt and Equity Securities, Reported at Less than Historical Cost |  |  |
Schedule of Available for sale Securities and Held to maturity Securities [Line Items] |  |  |
Historical cost | 81,482,000 | 398,172,000 |
Fair value of investments | $ 80,881,000 | $ 395,416,000 |
Percent of the Corporation's available for sale and held to maturity portfolio | 2.60% | 15.20% |
U.S. Government-Sponsored Mortgage-backed Securities |  |  |
Schedule of Available for sale Securities and Held to maturity Securities [Line Items] |  |  |
Unrealized losses on available for sale securities | $ 103,000 | $ 1,404,000 |
Available-for-sale number of securities in unrealized loss positions | instrument | 5 |  |
Unrealized losses in held to maturity portfolios | $ 107,000 | 401,000 |
Held-to-maturity, number of securities in unrealized loss positions | instrument | 3 |  |
State and municipal securities |  |  |
Schedule of Available for sale Securities and Held to maturity Securities [Line Items] |  |  |
Unrealized losses on available for sale securities | $ 246,000 | 807,000 |
Available-for-sale number of securities in unrealized loss positions | instrument | 4 |  |
Unrealized losses in held to maturity portfolios | $ 32,000 | 107,000 |
Held-to-maturity, number of securities in unrealized loss positions | instrument | 2 |  |
U.S. Government-sponsored agency securities |  |  |
Schedule of Available for sale Securities and Held to maturity Securities [Line Items] |  |  |
Unrealized losses on available for sale securities | $ 0 | 0 |
Unrealized losses in held to maturity portfolios | $ 113,000 | $ 37,000 |
Held-to-maturity, number of securities in unrealized loss positions | instrument | 2 |  |

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