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Investment Securities - Allowance for Credit Losses HTM (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items] |  |  |
Beginning balance | $ 0 |  |
Provision for credit loss expense | 2,546 | $ 0 | $ 0
Ending balance | 2,915 | 0 |
State and political subdivisions |  |  |
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items] |  |  |
Beginning balance | 0 |  |
Provision for credit loss expense | 2,249 |  |
Ending balance | 2,307 | 0 |
Other securities |  |  |
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items] |  |  |
Beginning balance | 0 |  |
Provision for credit loss expense | 297 |  |
Ending balance | 608 | 0 |
Impact of ASU 2016-13 adoption |  |  |
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items] |  |  |
Beginning balance | 369 |  |
Ending balance |  | 369 |
Impact of ASU 2016-13 adoption | State and political subdivisions |  |  |
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items] |  |  |
Beginning balance | 58 |  |
Ending balance |  | 58 |
Impact of ASU 2016-13 adoption | Other securities |  |  |
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items] |  |  |
Beginning balance | $ 311 |  |
Ending balance |  | $ 311 |

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- Definition Amount of allowance for credit loss for 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 (a) -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aaa) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=121599878&loc=SL82895884-210446 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=121599337&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=121599337&loc=SL82919249-210447 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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