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EMPLOYEE BENEFIT PLANS | 12 Months Ended
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Dec. 31, 2019
EMPLOYEE BENEFIT PLANS |
EMPLOYEE BENEFIT PLANS | 15.EMPLOYEE BENEFIT PLANS ​ Defined Contribution Plans—Eligible employees currently participate in a defined contribution profit sharing and savings plan ("PSSP") that we sponsor. The PSSP covers all regular full-time employees. PSSP participants may elect to make voluntary contributions to this plan up to a specified amount of their compensation. We make matching contributions based on a percent of an employee's eligible compensation and also make an additional non-matching contribution. Our contribution expense for the PSSP was approximately $21.1 million, $19.9 million and $18.7 million for the years ended December 31, 2019, 2018 and 2017, respectively. ​ Defined Benefit Plan—Eligible employees and former employees of certain of our mining operations participate in a defined benefit plan (the "Pension Plan") that we sponsor. The Pension Plan is closed to new applicants. Participants in the Pension Plan are no longer receiving benefit accruals for service. Participants can participate in enhanced benefits provisions under the PSSP. The benefit formula for the Pension Plan is a fixed-dollar unit based on years of service. ​ The following sets forth changes in benefit obligations and plan assets for the years ended December 31, 2019 and 2018 and the funded status of the Pension Plan reconciled with the amounts reported in our consolidated financial statements: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | December 31, | ​
​ | ​ | 2019 |  | 2018 |
​ | ​ | (dollars in thousands) | ​
Change in benefit obligations: | ​ | ​ | ​ | ​ | ​ | ​ | ​
Benefit obligations at beginning of year | ​ | $ | 118,958 | ​ | $ | 127,298 | ​
Interest cost | ​ |  | 4,864 | ​ |  | 4,462 | ​
Actuarial loss (gain) | ​ |  | 17,084 | ​ |  | (8,562) | ​
Benefits paid | ​ |  | (4,481) | ​ |  | (4,240) | ​
Benefit obligations at end of year | ​ |  | 136,425 | ​ |  | 118,958 | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Change in plan assets: | ​ | ​ | ​ | ​ | ​ | ​ | ​
Fair value of plan assets at beginning of year | ​ |  | 75,823 | ​ |  | 81,981 | ​
Employer contribution | ​ |  | 5,559 | ​ |  | 4,187 | ​
Actual return on plan assets | ​ |  | 14,666 | ​ |  | (6,105) | ​
Benefits paid | ​ |  | (4,481) | ​ |  | (4,240) | ​
Fair value of plan assets at end of year | ​ |  | 91,567 | ​ |  | 75,823 | ​
Funded status at the end of year | ​ | $ | (44,858) | ​ | $ | (43,135) | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Amounts recognized in balance sheet: | ​ | ​ | ​ | ​ | ​ | ​ | ​
Non-current liability | ​ | $ | (44,858) | ​ | $ | (43,135) | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Amounts recognized in accumulated other comprehensive income consists of: | ​ | ​ | ​ | ​ | ​ | ​ | ​
Prior service cost | ​ | $ | (940) | ​ | $ | (1,126) | ​
Net actuarial loss | ​ | ​ | (45,125) | ​ | ​ | (41,697) | ​
​ | ​ | $ | (46,065) | ​ | $ | (42,823) | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Weighted-average assumption to determine benefit obligations as of December 31, | ​ | ​ | ​ | ​ | ​ | ​ | ​
Discount rate | ​ |  | 3.15% | ​ |  | 4.17% | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Weighted-average assumptions used to determine net periodic benefit cost for the year ended December 31, | ​ | ​ | ​ | ​ | ​ | ​ | ​
Discount rate | ​ |  | 4.17% | ​ |  | 3.54% | ​
Expected return on plan assets | ​ |  | 6.50% | ​ |  | 7.00% | ​
​ The actuarial loss component of the change in benefit obligation in 2019 was primarily attributable to a decrease in the discount rate compared to December 31, 2018, offset in part by updated mortality tables. The actuarial gain component of the change in benefit obligation in 2018 was primarily attributable to an increase in the discount rate compared to December 31, 2017 and updated mortality tables, offset in part by decreases in expected retirements and other demographic changes. ​ The expected long-term rate of return used to determine our pension liability is based on a 1.5% active management premium in addition to an asset allocation assumption of: ​
​ | ​ | ​ | ​
​ | ​ | ​ | ​
​ | ​ | Asset allocation | ​
As of December 31, 2019 |  | assumption |
Equity securities | ​ | 62% | ​
Fixed income securities |  | 33% | ​
Real estate |  | 5% | ​
​ |  | 100% | ​
​ The actual return on plan assets was 19.2% and a loss of 6.7% for the years ended December 31, 2019 and 2018, respectively. ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended December 31, |
​ |  | 2019 |  | 2018 |  | 2017 | ​
​ | ​ | (in thousands) |
Components of net periodic benefit cost: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Interest cost | ​ | $ | 4,864 | ​ | $ | 4,462 | ​ | $ | 4,587 | ​
Expected return on plan assets | ​ |  | (4,932) | ​ |  | (5,784) | ​ |  | (4,978) | ​
Amortization of prior service cost | ​ | ​ | 186 | ​ | ​ | 186 | ​ | ​ | 186 | ​
Amortization of net loss | ​ |  | 3,922 | ​ |  | 3,608 | ​ |  | 3,054 | ​
Net periodic benefit cost (1) | ​ | $ | 4,040 | ​ | $ | 2,472 | ​ | $ | 2,849 | ​
(1) | Nonservice components of net periodic benefit cost are included in the Other income (expense) line item within our consolidated statements of income (see Note 2 – Summary of Significant Accounting Policies).
​ ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Year Ended December 31,
​ | ​ | 2019 |  | 2018 | ​
​ | ​ | (in thousands) | ​
Other changes in plan assets and benefit obligation recognized in accumulated other comprehensive loss: | ​ | ​ | ​ | ​ | ​ | ​ | ​
Net actuarial loss | ​ | $ | (7,350) | ​ | $ | (3,326) | ​
Reversal of amortization item: | ​ | ​ | ​ | ​ | ​ | ​ | ​
Prior service cost | ​ | ​ | 186 | ​ | ​ | 186 | ​
Net actuarial loss | ​ |  | 3,922 | ​ |  | 3,608 | ​
Total recognized in accumulated other comprehensive loss | ​ |  | (3,242) | ​ |  | 468 | ​
Net periodic benefit cost | ​ |  | (4,040) | ​ |  | (2,472) | ​
Total recognized in net periodic benefit cost and accumulated other comprehensive loss | ​ | $ | (7,282) | ​ | $ | (2,004) | ​
​ Estimated future benefit payments as of December 31, 2019 are as follows: ​
​ | ​ | ​ | ​ | ​
Year Ended | ​ | ​ | ​ | ​
December 31, |  | (in thousands) |
​ | ​ | ​ | ​ | ​
2020 | ​ | $ | 5,288 | ​
2021 | ​ |  | 5,677 | ​
2022 | ​ |  | 6,045 | ​
2023 | ​ |  | 6,342 | ​
2024 | ​ |  | 6,507 | ​
2025-2029 | ​ |  | 34,755 | ​
​ | ​ | $ | 64,614 | ​
​ We expect to contribute $5.3 million to the Pension Plan in 2020. ​ The Compensation Committee has appointed an investment manager with full investment authority with respect to Pension Plan investments subject to investment guidelines and compliance with ERISA or other applicable laws. The investment manager employs a series of asset allocation strategy phases to glide the portfolio risk commensurate with both plan characteristics and market conditions. The objective of the allocation policy is to reach and maintain fully funded status. The total portfolio allocation will be adjusted as the funded ratio of the Pension Plan changes and market conditions warrant. The target allocation includes investments in equity and fixed income commingled investment funds. Total account performance is reviewed at least annually, using a dynamic benchmark approach to track investment performance. General asset allocation guidelines at December 31, 2019 are as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Percentage of Total Portfolio |
​ |  | Minimum |  | Target |  | Maximum |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Equity securities | ​ | 45% | ​ | 62% | ​ | 80% | ​
Fixed income securities | ​ | 10% | ​ | 33% | ​ | 55% | ​
Real estate | ​ | 0% | ​ | 5% | ​ | 10% | ​
​ Equity securities include domestic equity securities, developed international securities, emerging markets equity securities and real estate investment trust. Fixed income securities include domestic and international investment grade fixed income securities, high yield securities and emerging markets fixed income securities. Fixed income futures may also be utilized within the fixed income securities asset allocation. ​ The following information discloses the fair values of our Pension Plan assets by asset category: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | December 31, |
​ | ​ | 2019 | ​ | 2018 | ​
​ | ​ | (in thousands) |
Cash and cash equivalents (a) | ​ | $ | 2,958 | ​ | $ | 5,277 | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Commingled investment funds measured at net asset value (b): | ​ | ​ | ​ | ​ | ​ | ​ | ​
Equities - Global | ​ | ​ | 10,028 | ​ | ​ | — | ​
Equities - United States large-cap | ​ | ​ | 19,220 | ​ | ​ | 21,862 | ​
Equities - United States small-cap | ​ | ​ | 7,592 | ​ | ​ | 5,259 | ​
Equities - International developed markets | ​ | ​ | 10,528 | ​ | ​ | 10,593 | ​
Equities - International emerging markets | ​ | ​ | 8,410 | ​ | ​ | 4,808 | ​
Fixed income - Investment grade | ​ | ​ | 26,186 | ​ | ​ | 15,777 | ​
Fixed income - High yield | ​ | ​ | — | ​ | ​ | 4,508 | ​
Real estate | ​ | ​ | 4,355 | ​ | ​ | 5,034 | ​
Other | ​ | ​ | 2,290 | ​ | ​ | 2,705 | ​
Total | ​ | $ | 91,567 | ​ | $ | 75,823 | ​
(a) | Cash and cash equivalents represents a Level 1 fair value measurement. See Note 2 – Summary of Significant Accounting Policies – Fair Value Measurements for more information regarding the definitions of fair value hierarchy levels.
(b) | Investments measured at fair value using the net asset value per share (or its equivalent) have not been classified within the fair value hierarchy. The fair values of all commingled investment funds are determined based on the net asset values per unit of each of the funds. The net asset values per unit represent the aggregate value of the fund's assets at fair value less liabilities, divided by the number of units outstanding.
​ See Note 2 – Summary of Significant Accounting Policies for more information on our accounting policy for pension benefits.

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