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BENEFIT PLANS (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | ---
Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Sep. 30, 2016 | Sep. 30, 2017 | Sep. 30, 2016 | May 12, 2017 | Dec. 31, 2016
Pension Benefits [Member] |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |
Defined Benefit Plan, Tax Status [Extensible List] | us-gaap:QualifiedPlanMember |  |  |  | us-gaap:QualifiedPlanMember |  |  |
Unamortized actuarial gain |  |  |  |  |  |  | $ 1,900 |
Discount rate |  |  |  |  |  |  | 4.40% | 4.50%
Employer contributions |  |  | $ 2,900 |  |  |  |  |
Net periodic benefit cost [Abstract] |  |  |  |  |  |  |  |
Service cost | $ 1,037 |  |  | $ 1,027 | $ 3,143 | $ 3,079 |  |
Interest cost | 1,453 |  |  | 1,406 | 4,265 | 4,218 |  |
Expected return on plan assets | (3,448) |  |  | (2,961) | (9,977) | (8,882) |  |
Amortization of unrecognized net loss | 148 |  |  | 377 | 619 | 1,131 |  |
Amortization of prior service cost | 13 |  |  | 11 | 43 | 33 |  |
Net periodic benefit cost (income) | (797) |  |  | (140) | (1,907) | (421) |  |
Post-retirement Benefits [Member] |  |  |  |  |  |  |  |
Net periodic benefit cost [Abstract] |  |  |  |  |  |  |  |
Service cost | 0 |  |  | 0 | 0 | 0 |  |
Interest cost | 19 |  |  | 20 | 57 | 61 |  |
Expected return on plan assets | 0 |  |  | 0 | 0 | 0 |  |
Amortization of unrecognized net loss | 2 |  |  | (1) | 6 | (4) |  |
Amortization of prior service cost | (45) |  |  | (45) | (134) | (134) |  |
Net periodic benefit cost (income) | $ (24) |  |  | $ (26) | $ (71) | $ (77) |  |
Merchants Bancshares, Inc. [Member] | Pension Benefits [Member] |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |
Employer contributions |  | $ 2,000 |  |  |  |  |  |

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- Definition Amount, after tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669686-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(4) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(5) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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