EMPLOYEE BENEFIT PLANS Narrative 1 (Details) - USD ($) $ in Millions |
12 Months Ended | |||
|---|---|---|---|---|
Mar. 01, 2016 |
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Defined Benefit Plan Disclosure [Line Items] | ||||
| Thrift Plan, description | The NuStar Thrift Plan (the Thrift Plan) is a qualified defined contribution plan that became effective June 26, 2006. Participation in the Thrift Plan is voluntary and open to substantially all our domestic employees upon their dates of hire. Thrift Plan participants can contribute from 1% up to 30% of their total annual compensation to the Thrift Plan in the form of pre-tax and/or after tax employee contributions. We make matching contributions in an amount equal to 100% of each participant’s employee contributions up to a maximum of 6% of the participant’s total annual compensation. | |||
| Thrift Plan matching contributions | $ 6.9 | $ 6.6 | $ 6.3 | |
| Benefit plan costs, international employees | $ 2.5 | 2.4 | $ 2.6 | |
| Pension Plan, description | 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. Under the cash balance formula, benefits are determined based on age, service and interest credits, and employees become fully vested in their benefits upon attaining three years of vesting service. Prior to January 1, 2014, eligible employees were covered under either a cash balance formula or a final average pay formula (FAP). Effective January 1, 2014, the Pension Plan was amended to freeze the FAP benefits as of December 31, 2013, and going forward, all eligible employees are covered under the cash balance formula discussed above. | |||
| Defined benefit plan, assumptions used in calculations description | We amortize prior service costs and credits on a straight-line basis over the average remaining service period of employees expected to receive benefits under our Pension Plans and other postretirement benefit plans (“Amortization of prior service credit” in table above). We amortize the actuarial gains and losses that exceed 10 percent of the greater of the projected benefit obligation or market-related value of plan assets (smoothed asset value) over the average remaining service period of active employees expected to receive benefits under our Pension Plans and other postretirement benefit plans (“Amortization of net actuarial loss” in table above). | |||
| Pension Plans (The Pension Plan, Excess Pension Plan and SERP) [Member] | ||||
| Defined Benefit Plan Disclosure [Line Items] | ||||
| Employee benefit plans obligations assumed | $ 22.5 | |||
| Accumulated benefit obligation for the Pension Plans | $ 146.3 | $ 125.0 | ||
| Other Postretirement Benefits Plan [Member] | ||||
| Defined Benefit Plan Disclosure [Line Items] | ||||
| Employee benefit plans obligations assumed | $ 10.2 | |||