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Investment Securities - Amortized Cost of Debt Securities Held-to-Maturity (Details) - USD ($) $ in Thousands | Mar. 31, 2021 | Dec. 31, 2020
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Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items] |  |
Amortized cost, held to maturity | $ 260,454 | $ 284,563
AAA/AA/A |  |
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items] |  |
Amortized cost, held to maturity | 260,454 | 284,563
BBB/BB/B |  |
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items] |  |
Amortized cost, held to maturity | 0 | 0
Obligations of U.S. government agencies | AAA/AA/A |  |
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items] |  |
Amortized cost, held to maturity | 250,178 | 273,667
Obligations of U.S. government agencies | BBB/BB/B |  |
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items] |  |
Amortized cost, held to maturity | 0 | 0
Obligations of states and political subdivisions | AAA/AA/A |  |
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items] |  |
Amortized cost, held to maturity | 10,276 | 10,896
Obligations of states and political subdivisions | BBB/BB/B |  |
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items] |  |
Amortized cost, held to maturity | $ 0 | $ 0

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- Definition Amount of 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 320 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26610-111562 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27232-111563 + Details
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