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Workers' Compensation And Pneumoconiosis (Tables) | 9 Months Ended
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Sep. 30, 2025
Defined Benefit Plan Disclosure [Line Items] |
Reconciliation of changes in workers' compensation liability | The changes in the workers’ compensation liability, including current and long-term liability balances, for each of the periods presented were as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Three Months Ended | ​ | Nine Months Ended |
​ | ​ | September 30, | ​ | September 30, | ​
​ | ​ | 2025 |  | 2024 |  | 2025 |  | 2024 | ​
​ | ​ | (in thousands) | ​
Beginning balance | ​ | $ | 49,234 | ​ | $ | 47,194 | ​ | $ | 47,870 | ​ | $ | 47,975 | ​
Changes in accruals | ​ |  | 3,418 | ​ |  | 3,658 | ​ |  | 10,213 | ​ |  | 10,148 | ​
Payments | ​ |  | (3,608) | ​ |  | (3,784) | ​ |  | (10,672) | ​ |  | (11,278) | ​
Interest accretion | ​ |  | 569 | ​ |  | 509 | ​ |  | 1,706 | ​ |  | 1,527 | ​
Valuation loss (gain) (1) | ​ |  | — | ​ | ​ | — | ​ |  | 496 | ​ | ​ | (795) | ​
Ending balance | ​ | $ | 49,613 | ​ | $ | 47,577 | ​ | $ | 49,613 | ​ | $ | 47,577 | ​
(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 loss in 2025 is due to a decrease in the discount rate from 5.17% on December 31, 2024 to 4.92% on June 30, 2025. The valuation gain in 2024 is due to an increase in the discount rate from 4.66% on December 31, 2023 to 5.18% on June 30, 2024.
Pneumoconiosis benefits |
Defined Benefit Plan Disclosure [Line Items] |
Components of net periodic benefit cost |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Three Months Ended | ​ | Nine Months Ended | ​
​ | ​ | September 30, | ​ | September 30, | ​
​ | ​ | 2025 |  | 2024 |  | 2025 |  | 2024 |
​ | ​ | (in thousands) | ​
Service cost | ​ | $ | 864 | ​ | $ | 864 | ​ | $ | 2,612 | ​ | $ | 2,583 |
Interest cost (1) | ​ |  | 1,677 | ​ |  | 1,558 | ​ |  | 5,029 | ​ |  | 4,674 | ​
Net amortization (1) | ​ |  | 232 | ​ |  | 839 | ​ |  | 696 | ​ |  | 2,517 | ​
Net periodic benefit cost | ​ | $ | 2,773 | ​ | $ | 3,261 | ​ | $ | 8,337 | ​ | $ | 9,774 | ​
(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 changes in the liability for workers' compensation during the period. + 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 -Topic 715 -SubTopic 20 -Subparagraph (h) -Name Accounting Standards Codification -Paragraph 1 -Section 50 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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