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EMPLOYEE BENEFIT PLANS | 3 Months Ended
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Mar. 31, 2018
Retirement Benefits [Abstract] |
EMPLOYEE BENEFIT PLANS | EMPLOYEE BENEFIT PLANS The NuStar Pension Plan (the Pension Plan) is a qualified non-contributory defined benefit pension plan that provides eligible U.S. employees with retirement income as calculated under a cash balance formula. The NuStar Excess Pension Plan (the Excess Pension Plan) is a nonqualified deferred compensation plan that provides benefits to a select group of management or other highly compensated employees. The Pension Plan and Excess Pension Plan are collectively referred to as the Pension Plans. We also sponsor a contributory medical benefits plan for U.S. employees that retired prior to April 1, 2014. For employees that retire on or after April 1, 2014, we provide partial reimbursement for eligible third-party health care premiums. 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 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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