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ACQUISITIONS, Intangible Asset, Goodwill and Acquisition-related Expenses (Details) - USD ($) $ in Thousands |  | 12 Months Ended
--- | --- | ---
Jul. 12, 2019 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Fair Value of Subordinated Notes Payable [Abstract] |  |  |  |
Subordinated notes |  | $ 13,795 | $ 0 |
Summary of loans acquired [Abstract] |  |  |  |
Merger and acquisition integration related (recoveries) expenses |  | $ 8,608 | $ (769) | $ 25,986
Kinderhook Bank Corp [Member] | Core Deposits [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Estimated useful life |  | 8 years |  |
Kinderhook Bank Corp [Member] | Other Intangibles [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Estimated useful life |  | 8 years |  |
Kinderhook Bank Corp [Member] | Subordinated Notes Maturing in February 2028 [Member] |  |  |  |
Fair Value of Subordinated Notes Payable [Abstract] |  |  |  |
Subordinated notes | $ 3,000 |  |  |
Fixed interest rate percentage | 6.00% |  |  |
Maturity date | Feb. 29, 2028 |  |  |
Kinderhook Bank Corp [Member] | Subordinated Notes Maturing in November 2025 [Member] |  |  |  |
Fair Value of Subordinated Notes Payable [Abstract] |  |  |  |
Subordinated notes | $ 10,000 |  |  |
Fixed interest rate percentage | 6.375% |  |  |
Maturity date | Nov. 30, 2025 |  |  |
Penna & Associates Agency, Inc. [Member] | Core Deposits [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Estimated useful life |  | 8 years |  |
Penna & Associates Agency, Inc. [Member] | Other Intangibles [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Estimated useful life |  | 8 years |  |
Styles Bridges Associates [Member] | Core Deposits [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Estimated useful life |  | 8 years |  |
Styles Bridges Associates [Member] | Other Intangibles [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Estimated useful life |  | 8 years |  |
HR Consultants (SA), LLC [Member] | Core Deposits [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Estimated useful life |  | 8 years |  |
HR Consultants (SA), LLC [Member] | Other Intangibles [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Estimated useful life |  | 8 years |  |
Merchants Bancshares, Inc. [Member] | Core Deposits [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Estimated useful life |  | 8 years |  |
Merchants Bancshares, Inc. [Member] | Other Intangibles [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Estimated useful life |  | 8 years |  |
Dryfoos [Member] | Core Deposits [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Estimated useful life |  | 8 years |  |
Dryfoos [Member] | Other Intangibles [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Estimated useful life |  | 8 years |  |
BAS [Member] | Core Deposits [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Estimated useful life |  | 8 years |  |
BAS [Member] | Other Intangibles [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Estimated useful life |  | 8 years |  |
Northeast Capital Management, Inc [Member] | Core Deposits [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Estimated useful life |  | 8 years |  |
Northeast Capital Management, Inc [Member] | Other Intangibles [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Estimated useful life |  | 8 years |  |
Gordon B. Roberts Agency, Inc [Member] | Core Deposits [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Estimated useful life |  | 8 years |  |
Gordon B. Roberts Agency, Inc [Member] | Other Intangibles [Member] |  |  |  |
Intangible Assets [Abstract] |  |  |  |
Estimated useful life |  | 8 years |  |

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