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WORKERS' COMPENSATION AND PNEUMOCONIOSIS (Tables) | 3 Months Ended
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Mar. 31, 2021
Accrued Workers Compensation And Pneumoconiosis Benefits |
Reconciliation of changes in workers' compensation liability | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Three Months Ended |
​ | ​ | March 31, | ​
​ | ​ | 2021 |  | 2020 | ​
​ | ​ | (in thousands) | ​
Beginning balance | ​ | $ | 54,739 | ​ | $ | 53,384 | ​
Accruals increase | ​ |  | 1,672 | ​ |  | 1,748 | ​
Payments | ​ |  | (2,410) | ​ |  | (2,571) | ​
Interest accretion | ​ |  | 232 | ​ |  | 319 | ​
Ending balance | ​ | $ | 54,233 | ​ | $ | 52,880 | ​
Pneumoconiosis benefits |
Accrued Workers Compensation And Pneumoconiosis Benefits |
Components of net periodic benefit cost |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Three Months Ended | ​
​ | ​ | March 31, | ​
​ | ​ | 2021 |  | 2020 |
​ | ​ | (in thousands) | ​
Service cost | ​ | $ | 1,031 | ​ | $ | 878 |
Interest cost (1) | ​ |  | 636 | ​ |  | 750 | ​
Net amortization (1) | ​ |  | 1,043 | ​ |  | (172) | ​
Net periodic benefit cost | ​ | $ | 2,710 | ​ | $ | 1,456 | ​
(1) | Interest cost and net amortization are included in the Other expense line item within our condensed consolidated statements of income.

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- Definition Tabular disclosure of the changes in the liability for workers' compensation during the period. + References No definition available. + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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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 http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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