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ACQUISITIONS - Intangible Asset, Goodwill and Acquisition-related Expenses (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020
Summary of loans acquired [Abstract] |  |  |  |
Merger and acquisition integration related (recoveries) expenses | $ 102 | $ 796 | $ 133 | $ 4,537
Steuben Trust Corporation [Member] | Other intangibles |  |  |  |
Finite-Lived Intangible Assets, Net [Abstract] |  |  |  |
Intangible asset useful life (amortization period) |  |  | 8 years |
NuVantage Insurance Corporation [Member] | Core deposit intangibles |  |  |  |
Finite-Lived Intangible Assets, Net [Abstract] |  |  |  |
Intangible asset useful life (amortization period) |  |  | 8 years |
Fringe Benefits Design of Minnesota, Inc ("FBD") [Member] | Other intangibles |  |  |  |
Finite-Lived Intangible Assets, Net [Abstract] |  |  |  |
Intangible asset useful life (amortization period) |  |  | 15 years |
Thomas Gregory Associates [Member] | Other intangibles |  |  |  |
Finite-Lived Intangible Assets, Net [Abstract] |  |  |  |
Intangible asset useful life (amortization period) |  |  | 13 years |

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- Definition This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 25 -Paragraph 23 -URI http://asc.fasb.org/extlink&oid=123586518&loc=d3e1043-128460 + Details
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- Definition Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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