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Investment Securities - Investments in Debt and Equity Securities Reported Less than Historical Cost (Details) - USD ($) $ in Thousands | Jun. 30, 2020 | Dec. 31, 2019
--- | --- | ---
Schedule of Investments [Line Items] |  |
Fair value | $ 51,815 | $ 395,416
Investments reported at less than historical cost |  |
Schedule of Investments [Line Items] |  |
Historical cost | 52,054 | 398,172
Fair value | 51,815 | 395,416
Gross unrealized losses | $ 239 | $ 2,756
Percent of the Corporation's investment portfolio | 1.90% | 15.20%

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