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WORKERS' COMPENSATION AND PNEUMOCONIOSIS (Tables) | 6 Months Ended
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Jun. 30, 2022
Black lung benefits: |
Reconciliation of changes in workers' compensation liability | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Three Months Ended | ​ | Six Months Ended |
​ | ​ | June 30, | ​ | June 30, | ​
​ | ​ | 2022 |  | 2021 |  | 2022 |  | 2021 | ​
​ | ​ | (in thousands) | ​
Beginning balance | ​ | $ | 53,206 | ​ | $ | 54,233 | ​ | $ | 53,448 | ​ | $ | 54,739 | ​
Accruals increase | ​ |  | 2,271 | ​ |  | 1,565 | ​ |  | 4,546 | ​ |  | 3,237 | ​
Payments | ​ |  | (3,278) | ​ |  | (2,565) | ​ |  | (6,082) | ​ |  | (4,975) | ​
Interest accretion | ​ |  | 287 | ​ |  | 231 | ​ |  | 574 | ​ |  | 463 | ​
Valuation gain (1) | ​ |  | (5,265) | ​ |  | (1,405) | ​ |  | (5,265) | ​ |  | (1,405) | ​
Ending balance | ​ | $ | 47,221 | ​ | $ | 52,059 | ​ | $ | 47,221 | ​ | $ | 52,059 | ​
(1) | Our estimate of the liability for the present value of current workers′ compensation benefits is based on our actuarial calculations. Our actuarial calculations are based on a blend of actuarial projection methods and numerous
| assumptions including claims development patterns, mortality, medical costs and interest rates. The valuation gain in 2022 is due to an increase in the discount rate from 2.41% on December 31, 2021 to 4.22% on June 30, 2022. The valuation gain in 2021 is due to an increase in the discount rate from 1.95% on December 31, 2020 to 2.34% on June 30, 2021.
Pneumoconiosis benefits |
Black lung benefits: |
Components of net periodic benefit cost |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Three Months Ended | ​ | Six Months Ended | ​
​ | ​ | June 30, | ​ | June 30, | ​
​ | ​ | 2022 |  | 2021 |  | 2022 |  | 2021 |
​ | ​ | (in thousands) | ​
Service cost | ​ | $ | 954 | ​ | $ | 989 | ​ | $ | 1,901 | ​ | $ | 2,020 |
Interest cost (1) | ​ |  | 749 | ​ |  | 637 | ​ |  | 1,496 | ​ |  | 1,273 | ​
Net amortization (1) | ​ |  | 259 | ​ |  | 1,043 | ​ |  | 519 | ​ |  | 2,086 | ​
Net periodic benefit cost | ​ | $ | 1,962 | ​ | $ | 2,669 | ​ | $ | 3,916 | ​ | $ | 5,379 | ​
(1) | Interest cost and net amortization are included in the Other income (expense) line item within our condensed consolidated statements of income.

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- Definition Tabular disclosure of the components of net benefit costs for pension plans and/or other employee benefit plans including service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) recognized due to settlements or curtailments. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h) -URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 + Details
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