v3.8.0.1

EMPLOYEE BENEFIT PLANS (Tables) | 3 Months Ended
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Mar. 31, 2018
Retirement Benefits [Abstract] |
Schedule of Net Benefit Costs [Table Text Block] | The components of net periodic benefit cost (income) related to our Pension Plans and other postretirement benefit plans were as follows:
| Pension Plans |  | Other Postretirement Benefit Plans
| 2018 |  | 2017 |  | 2018 |  | 2017
| (Thousands of Dollars)
For the three months ended March 31: |  |  |  |  |  |  |
Service cost | $ | 2,406 |  |  | $ | 2,239 |  |  | $ | 126 |  |  | $ | 113 |
Interest cost | 1,206 |  |  | 1,127 |  |  | 108 |  |  | 108 |
Expected return on assets | (1,855 | ) |  | (1,603 | ) |  | — |  |  | — |
Amortization of prior service credit | (514 | ) |  | (515 | ) |  | (287 | ) |  | (286 | )
Amortization of net loss | 544 |  |  | 371 |  |  | 54 |  |  | 48 |
Net periodic benefit cost (income) | $ | 1,787 |  |  | $ | 1,619 |  |  | $ | 1 |  |  | $ | (17 | )

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- Definition Tabular disclosure of the components of net benefit costs for pension plans and/or other employee benefit plans including service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) recognized due to settlements or curtailments. + 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) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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