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Investment Securities - Allowance for Credit Losses HTM (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items] |  |  |  |
Beginning balance | $ 1,132 | $ 307 | $ 2,915 | $ 0
Provision for credit loss expense | 0 | 66 | (1,183) | 4
Securities charged-off |  |  | (600) |
Recoveries | 147 |  | 147 |
Ending balance | 1,279 | 373 | 1,279 | 373
State and political subdivisions |  |  |  |
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items] |  |  |  |
Beginning balance | 871 | 95 | 2,307 | 0
Provision for credit loss expense | 325 | (22) | (1,111) | 15
Securities charged-off |  |  | 0 |
Recoveries | 0 |  | 0 |
Ending balance | 1,196 | 73 | 1,196 | 73
Other securities |  |  |  |
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items] |  |  |  |
Beginning balance | 261 | 212 | 608 | 0
Provision for credit loss expense | (325) | 88 | (72) | (11)
Securities charged-off |  |  | (600) |
Recoveries | 147 |  | 147 |
Ending balance | $ 83 | $ 300 | $ 83 | 300
Cumulative Effect, Period of Adoption, Adjustment |  |  |  |
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items] |  |  |  |
Beginning balance |  |  |  | 369
Cumulative Effect, Period of Adoption, Adjustment | State and political subdivisions |  |  |  |
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items] |  |  |  |
Beginning balance |  |  |  | 58
Cumulative Effect, Period of Adoption, Adjustment | Other securities |  |  |  |
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items] |  |  |  |
Beginning balance |  |  |  | $ 311

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- Definition Amount, excluding accrued interest, of allowance for credit loss on investment in debt security measured at amortized cost (held-to-maturity). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446 + Details
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- Definition Amount of increase in allowance for credit loss on investment in debt security measured at amortized cost (held-to-maturity), from recovery. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447 + Details
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- Definition Amount of writeoff of investment in debt security, measured at amortized cost (held-to-maturity), charged against allowance for credit loss. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447 + Details
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- Definition Amount of expense (reversal of expense) for expected credit loss on investment in debt security measured at amortized cost (held-to-maturity). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447 + Details
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