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EMPLOYEE BENEFIT PLANS EMPLOYEE BENEFIT PLANS (Notes) | 9 Months Ended
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Sep. 30, 2019
Defined Benefit Plan [Abstract] |
EMPLOYEE BENEFIT PLANS | EMPLOYEE BENEFIT PLANS The following tables set forth the components of net periodic benefit cost (income) for our retirement and other postretirement benefit plans for the periods indicated:
| Retirement Benefits
| Three Months Ended |  | Nine Months Ended
| September 30, |  | September 30,
| 2019 |  | 2018 |  | 2019 |  | 2018
| (Thousands of dollars)
Components of net periodic benefit cost |  |  |  |  |  |  |  |
Service cost | $ | 1,954 |  |  | $ | 1,832 |  |  | $ | 5,862 |  |  | $ | 5,496 |
Interest cost | 5,126 |  |  | 4,408 |  |  | 15,378 |  |  | 13,224 |
Expected return on plan assets | (5,892 | ) |  | (5,969 | ) |  | (17,676 | ) |  | (17,907 | )
Amortization of net loss | 3,158 |  |  | 4,258 |  |  | 9,474 |  |  | 12,774 |
Net periodic benefit cost | $ | 4,346 |  |  | $ | 4,529 |  |  | $ | 13,038 |  |  | $ | 13,587 |
| Other Postretirement Benefits
| Three Months Ended |  | Nine Months Ended
| September 30, |  | September 30,
| 2019 |  | 2018 |  | 2019 |  | 2018
| (Thousands of dollars)
Components of net periodic benefit cost |  |  |  |  |  |  |
Service cost | $ | 117 |  |  | $ | 211 |  |  | $ | 351 |  |  | $ | 633 |
Interest cost | 509 |  |  | 527 |  |  | 1,527 |  |  | 1,581 |
Expected return on plan assets | (570 | ) |  | (672 | ) |  | (1,710 | ) |  | (2,016 | )
Amortization of prior service credit | (57 | ) |  | (415 | ) |  | (171 | ) |  | (1,245 | )
Amortization of net loss | 74 |  |  | 334 |  |  | 222 |  |  | 1,002 |
Net periodic benefit cost (income) | $ | 73 |  |  | $ | (15 | ) |  | $ | 219 |  |  | $ | (45 | )

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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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -URI http://asc.fasb.org/topic&trid=2235017 + Details
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