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RETIREMENT PLANS - Rate Assumptions (Details) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
One-percentage change in assumed health care cost trend rates |  |  |
Accumulated postretirement benefit obligation, At trend | $ 5,308,000 | $ 5,108,000 |
Accumulated postretirement benefit obligation, At trend +1% | 5,723,000 | 5,487,000 |
Impact of Accumulated postretirement benefit obligation, At trend +1% | $ 415,000 | $ 379,000 |
Impact of Accumulated postretirement benefit obligation, At trend +1% (as a percent) | 7.80% | 7.40% |
Accumulated postretirement benefit obligation, At trend -1% | $ 4,944,000 | $ 4,775,000 |
Impact of Accumulated postretirement benefit obligation, At trend -1% | $ (364,000) | $ (333,000) |
Impact of Accumulated postretirement benefit obligation, At trend -1% (as a percent) | (6.90%) | (6.50%) |
Service cost plus interest cost, At trend | $ 389,000 | $ 194,000 |
Service cost plus interest cost, At Trend +1% | 429,000 | 214,000 |
Impact of Service cost plus interest cost, At trend +1% | 40,000 | 20,000 |
Impact of Service cost plus interest cost, At trend +1% (as a percent) | 10.3 | 10.3 |
Service cost plus interest cost, At Trend -1% | 355,000 | 177,000 |
Impact of Service cost plus interest cost, At trend -1% | $ (34,000) | $ (17,000) |
Impact of Service cost plus interest cost, At trend -1% (as a percent) | (8.70%) | (8.80%) |
Pension Plans |  |  |
Weighted-average rates assumed in the actuarial calculations for the pension plan |  |  |
Discount rate (as a percent) | 4.60% | 4.30% | 5.80%
Annual salary increase (as a percent) | 6.50% | 6.50% | 6.50%
Expected long-term return on plan assets (as a percent) | 6.10% | 6.30% | 6.50%
Postretirement Benefits |  |  |
Weighted-average rates assumed in the actuarial calculations for the pension plan |  |  |
Discount rate (as a percent) | 4.30% | 3.90% |
Postretirement Benefits | Medical benefit plan |  |  |
Health care cost trend rates |  |  |
2018 Trend rate | 5.30% |  |
2018 Ultimate rate | 4.50% |  |
Postretirement Benefits | Dental benefit plan |  |  |
Health care cost trend rates |  |  |
2018 Trend rate | 4.00% |  |
2018 Ultimate rate | 2.00% |  |

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- Definition For defined benefit pension plans, the actuarial present value of benefits decreased one percentage point attributed by the pension benefit formula to employee service rendered before a specified date and based on employee service and compensation (if applicable) before that date. + References No definition available. + Details
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- Definition For defined benefit pension plans, the actuarial present value of benefits increased one percentage point attributed by the pension benefit formula to employee service rendered before a specified date and based on employee service and compensation (if applicable) before that date. + References No definition available. + Details
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- Definition Percent of effect of a one-percentage-point decrease in the assumed health care cost trend rates on the aggregate of the service and interest cost components of net periodic postretirement health care benefit costs. + References No definition available. + Details
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- Definition Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level. + 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 (e) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost 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)(3) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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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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