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EMPLOYEE BENEFIT PLANS EMPLOYEE BENEFIT PLANS (Notes) | 9 Months Ended
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Sep. 30, 2018
Defined Benefit Plan [Abstract] |
EMPLOYEE BENEFIT PLANS | EMPLOYEE BENEFIT PLANS The following tables set forth the components of net periodic benefit cost for our pension and postretirement benefit plans for the periods indicated:
| Pension Benefits
| Three Months Ended |  | Nine Months Ended
| September 30, |  | September 30,
| 2018 |  | 2017 |  | 2018 |  | 2017
| (Thousands of dollars)
Components of net periodic benefit cost |  |  |  |  |  |  |
Service cost | $ | 1,832 |  |  | $ | 1,721 |  |  | $ | 5,496 |  |  | $ | 5,165 |
Interest cost | 4,408 |  |  | 4,655 |  |  | 13,224 |  |  | 13,965 |
Expected return on plan assets | (5,969 | ) |  | (5,336 | ) |  | (17,907 | ) |  | (16,008 | )
Amortization of net loss | 4,258 |  |  | 3,392 |  |  | 12,774 |  |  | 10,176 |
Net periodic benefit cost | $ | 4,529 |  |  | $ | 4,432 |  |  | $ | 13,587 |  |  | $ | 13,298 |
| Postretirement Benefits
| Three Months Ended |  | Nine Months Ended
| September 30, |  | September 30,
| 2018 |  | 2017 |  | 2018 |  | 2017
| (Thousands of dollars)
Components of net periodic benefit cost |  |  |  |  |  |  |
Service cost | $ | 211 |  |  | $ | 165 |  |  | $ | 633 |  |  | $ | 495 |
Interest cost | 527 |  |  | 565 |  |  | 1,581 |  |  | 1,695 |
Expected return on plan assets | (672 | ) |  | (564 | ) |  | (2,016 | ) |  | (1,692 | )
Amortization of prior service credit | (415 | ) |  | (415 | ) |  | (1,245 | ) |  | (1,245 | )
Amortization of net loss | 334 |  |  | 419 |  |  | 1,002 |  |  | 1,259 |
Net periodic benefit cost (income) | $ | (15 | ) |  | $ | 170 |  |  | $ | (45 | ) |  | $ | 512 |

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- References No definition available. + Details
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- Definition The entire disclosure for pension and other postretirement benefits. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -URI http://asc.fasb.org/topic&trid=2235017 + Details
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