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EMPLOYEE BENEFIT PLANS (Plans) (Details) $ in Thousands | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Mar. 31, 2017 USD ($) person | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($)
Nonunion Defined Benefit Pension Plan |  |  |
Nonunion Defined Benefit Pension, Supplemental Benefit, and Postretirement Health Benefit Plans |  |  |
Premium paid to purchase nonparticipating annuity contract | $ 7,600 | $ 7,600 |
Number of plan participants for which vested pension benefits were settled | person | 50 |  |
Unrecognized net actuarial loss |  | $ 22,588 | $ 23,294
Amortization period for unrecognized net actuarial loss |  | 8 years |
Lump-sum distributions |  | $ 18,700 |
Postretirement Health Benefit Plan |  |  |
Nonunion Defined Benefit Pension, Supplemental Benefit, and Postretirement Health Benefit Plans |  |  |
Unrecognized net actuarial loss |  | $ 2,764 | $ 5,708
Unrecognized prior service credit, amortization period |  | 9 years |

X
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- Definition The amount of lump sum benefit distributions paid. + References No definition available. + Details
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- Definition The period over which the unrecognized prior service cost (credit) is being amortized. + References No definition available. + Details
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- Definition Number of participants and beneficiaries for which vested benefit obligations were settled with nonparticipating annuity contract. + References No definition available. + Details
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- Definition Amount, before 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 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 2: 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 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Details
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