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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Postretirement Benefits (Details) | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Pension Plan |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Normal retirement benefit as percentage of final average compensation (in hundredths) | 1.20% |
Number of consecutive years considered in final average compensation | 5 years |
Number of prior years considered in final average compensation | 10 years |
Maximum service period | 25 years |
Normal retirement additional benefit | 1.00% |
Maximum additional service years | 10 years |
Percentage of average monthly compensation in excess of covered compensation for each year of credited service | 0.65% |
Maximum period of credited service | 35 years |
Covered compensation period | 35 years |
Other Postretirement Benefit Plan |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Contribution cost percentage | 50.00% |
Minimum age for eligibility before amendment | 55 years |
Contribution percentage before amendment | 40.00% |
Retiree premium percentage | 100.00% |
Cost of coverage contribution | 50.00% |
Premium contribution percentage after amendment | 50.00% |
Minimum | Other Postretirement Benefit Plan |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Retiree age group range | 55 years |
Maximum | Other Postretirement Benefit Plan |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Retiree age group range | 65 years |
Defined Contribution Profit Sharing, Savings and Investment Plan |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Defined contribution plan, employer non-discretionary contribution amount | 3.00% |
Contribution cost percentage | 50.00% |
Defined contribution plan, employer matching contribution, percent of employees' gross pay | 6.00% |
Defined Contribution Plan, Employer Contribution, Vesting Period |  | 5 years

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- Definition Percentage of contribution cost to be made by retirees, who are going to be continued under the coverage of plan. + References No definition available. + Details
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- Definition Percentage of contribution made under self-insure health care plan, before amendment. + References No definition available. + Details
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- Definition Percentage of contribution made under self-insure health care plan. + References No definition available. + Details
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- Definition The period for covered compensation, which is average of social security taxable wage bases in effect. + References No definition available. + Details
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- Definition Defined Contribution Plan, Employer Contribution, Vesting Period + References No definition available. + Details
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- Definition Defined Contribution Plan, Employer Non-Discretionary Contribution Amount + References No definition available. + Details
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- Definition Refers to maximum additional period considered in final average compensation, during which additional 1% of average monthly compensation for each additional year of service is added. + References No definition available. + Details
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- Definition Maximum period of credited service considered to apply excess of covered compensation for each year of credited service. + References No definition available. + Details
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- Definition Refers to maximum period considered in final average compensation. + References No definition available. + Details
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- Definition Minimum age for eligibility for coverage under self-insure health care plan, before amendment. + References No definition available. + Details
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- Definition Percentage of normal retirement benefit in terms of average monthly compensation resulting for each additional year. + References No definition available. + Details
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- Definition Percentage of normal retirement benefit in terms of final average compensation resulting from maximum period of 25 years. + References No definition available. + Details
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- Definition Refers to the percentage of average monthly compensation in excess of covered compensation for each year of credited service. + References No definition available. + Details
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- Definition Percentage of premium contribution made under self-insure health care plan. + References No definition available. + Details
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- Definition Eligible age of current and future retirees to be continued under coverage of plan. + References No definition available. + Details
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- Definition Percentage of premium to be paid by retiree under self-insure health care plan. + References No definition available. + 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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- Definition Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan. + References No definition available. + Details
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