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EMPLOYEE BENEFIT PLANS (Health care trend rates) (Details) - Postretirement Health Benefit Plan - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Assumed health care cost trend rates |  |
Health care cost trend rate assumed for next year (as a percent) |  | 8.00%
Rate to which the cost trend rate is assumed to decline (as a percent) |  | 4.50%
Year that the rate reaches the cost trend assumed rate |  | 2031
Effects of one-percentage-point change in assumed health care cost trend rates |  |
Effect of one-percentage-point increase on total of service and interest cost components | $ 335 |
Effect of one-percentage-point decrease on total of service and interest cost components | (262) |
Effect of one-percentage-point increase on postretirement benefit obligation | 4,820 |
Effect of one-percentage-point decrease on postretirement benefit obligation | $ (3,845) |
Pre-65 |  |
Assumed health care cost trend rates |  |
Health care cost trend rate assumed for next year (as a percent) | 8.30% |
Rate to which the cost trend rate is assumed to decline (as a percent) | 4.00% |
Year that the rate reaches the cost trend assumed rate | 2035 |
Post-65 |  |
Assumed health care cost trend rates |  |
Health care cost trend rate assumed for next year (as a percent) | 5.50% |
Rate to which the cost trend rate is assumed to decline (as a percent) | 4.00% |
Year that the rate reaches the cost trend assumed rate | 2024 |

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- Definition Amount of decrease in accumulated postretirement benefit obligation from one-percentage-point decrease in assumed health care cost trend rate. + 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 (m) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of decrease in service and interest cost components of net periodic postretirement benefit cost from one-percentage-point decrease in assumed health care cost trend rate. + 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 (m) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of increase in accumulated postretirement benefit obligation from one-percentage-point increase in assumed health care cost trend rate. + 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 (m) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of increase in service and interest cost components of net periodic postretirement benefit cost from one-percentage-point increase in assumed health care cost trend rate. + 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 (m) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Assumed rate, for next fiscal year, based on annual change in cost of health care cost benefits used to measure expected cost of benefits covered by defined benefit postretirement plan. Factors include, but are not limited to, estimate of health care inflation, change in health care utilization or delivery pattern, technological advances, and change in health status of participant. Excludes factors for change in composition of plan population by age and dependency status. + 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 (l) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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