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Debt Securities - Credit Quality Indicators for HTM Debt Securities (Details) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
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Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items] |  |
Debt securities, held-to-maturity | $ 189,836 | $ 224,611
US States and Political Subdivisions Debt Securities |  |
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items] |  |
Debt securities, held-to-maturity | 189,836 | 224,611
Moody's, Aaa Rating | Standard & Poor's, AAA Rating | US States and Political Subdivisions Debt Securities | Internal Investment Grade |  |
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items] |  |
Debt securities, held-to-maturity | 39,022 | 65,217
Moody's, Aa1, Aa2 or Aa3 Ratings | Standard & Poor's, AA+, AA or AA- Ratings | US States and Political Subdivisions Debt Securities | Internal Investment Grade |  |
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items] |  |
Debt securities, held-to-maturity | 123,664 | 130,316
Moody's, A1, A2 or A3 Ratings | Standard & Poor's, A+, A or A- Ratings | US States and Political Subdivisions Debt Securities | Internal Investment Grade |  |
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items] |  |
Debt securities, held-to-maturity | 27,150 | 28,689
Moody's, Not Rated | Standard & Poor's, Not Rated | US States and Political Subdivisions Debt Securities | Internal Investment Grade |  |
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items] |  |
Debt securities, held-to-maturity | $ 0 | $ 389

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