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LOANS AND ALLOWANCE FOR LOAN LOSSES - Troubled Debt Restructuring (Details) | 12 Months Ended
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Dec. 31, 2017 USD ($) loan | Dec. 31, 2016 USD ($) loan | Dec. 31, 2015 USD ($) loan
Trouble debt restructurings [Abstract] |  |  |
Recorded investment in troubled debt restructurings | $ 7,700,000 | $ 10,200,000 | $ 12,000,000
Specific reserves allocated for troubled debt restructuring | 700,000 | 900,000 | 1,400,000
Troubled debt restructurings accruing interest under modified terms | 1,700,000 | 5,800,000 | 7,600,000
Troubled debt restructurings on non-accrual status | 6,000,000 | 4,400,000 | 4,400,000
Additional amounts committed to customers with loans classified as troubled debt restructurings | $ 0 | 0 | $ 100,000
Additional amounts of interest and past due escrow payments capitalized |  | $ 4,000 |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | loan | 5 | 9 | 6
Pre-Modification Outstanding Recorded Investment | $ 948,000 | $ 854,000 | $ 3,287,000
Post-Modification Outstanding Recorded Investment | 948,000 | 769,000 | 3,287,000
Increase in allowance for loan losses related to troubled debt restructurings | 100,000 |  | 1,100,000
Troubled debt restructurings, charge offs (less than $0.1 million in 2014) | $ 0 | $ 0 | $ 0
Number of days past due after which a loan is considered to be in payment default | 90 days |  |
Financing receivable, modifications, subsequent default, number of loans | loan | 1 | 0 | 2
Financing receivable, modifications, subsequent default, recorded investment | $ 164,000 |  | $ 1,877,000
Commercial mortgages |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Financing receivable, modifications, subsequent default, number of loans | loan | 1 |  | 2
Financing receivable, modifications, subsequent default, recorded investment | $ 164,000 |  | $ 1,877,000
Residential Mortgages |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | loan |  | 2 |
Pre-Modification Outstanding Recorded Investment |  | $ 295,000 |
Post-Modification Outstanding Recorded Investment |  | $ 307,000 |
Home equity lines and loans |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | loan |  | 1 |
Pre-Modification Outstanding Recorded Investment |  | $ 74,000 |
Post-Modification Outstanding Recorded Investment |  | $ 74,000 |
Commercial mortgages: |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | loan |  | 1 |
Commercial mortgages: | Commercial mortgages |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | loan | 1 | 6 | 5
Pre-Modification Outstanding Recorded Investment | $ 166,000 | $ 485,000 | $ 2,810,000
Post-Modification Outstanding Recorded Investment | $ 166,000 | $ 388,000 | $ 2,810,000
Residential Mortgages |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | 1 |  |
Pre-Modification Outstanding Recorded Investment | $ 105,000 |  |
Post-Modification Outstanding Recorded Investment | $ 105,000 |  |
Consumer Loans | Home equity lines and loans |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans |  | 1 |
Extended Maturity |  |  |
Trouble debt restructurings [Abstract] |  |  |
Troubled debt restructuring, extension of maturity date, duration |  | 13 years |
Closing costs capitalized on restructured loan |  | $ 8,000 |
Extended Maturity, Interest Rate Below Market Reduction | Commercial mortgages: | Commercial mortgages |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | loan |  | 5 |
Payment Deferral |  |  |
Trouble debt restructurings [Abstract] |  |  |
Postponement or reduction, amortized payments, period |  | 3 months |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans |  |  | 5
Troubled debt restructurings, charge offs (less than $0.1 million in 2014) |  | $ 97,000 |
Interest Rate Below Market Reduction |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans |  |  | 2
Commercial and industrial |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | loan | 3 |  |
Pre-Modification Outstanding Recorded Investment | $ 677,000 |  |
Post-Modification Outstanding Recorded Investment | $ 677,000 |  |
Commercial and industrial | Commercial, and Agricultural |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | loan |  |  | 1
Pre-Modification Outstanding Recorded Investment |  |  | $ 477,000
Post-Modification Outstanding Recorded Investment |  |  | $ 477,000
Commercial and industrial | Principal Forgiveness | Commercial, and Agricultural |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | loan | 2 |  |
Commercial and industrial | Extended Maturity | Commercial, and Agricultural |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | loan | 1 |  |
Commercial and industrial | Loan Consolidation | Commercial, and Agricultural |  |  |
Loans by class modified as troubled debt restructurings [Abstract] |  |  |
Number of Loans | loan | 2 |  |

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