WORKERS' COMPENSATION AND PNEUMOCONIOSIS - Workers' Comp (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2023	Sep. 30, 2022	Jun. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2021
Reconciliation of changes in the workers' compensation liability
Beginning balance	$ 51,108	$ 47,221	$ 53,448	$ 49,452	$ 53,448
Changes in accruals	3,001	2,918		9,071	7,464
Payments	(3,503)	(2,856)		(10,008)	(8,938)
Interest accretion	551	287		1,652	861
Valuation loss (gain)				990	(5,265)
Ending balance	51,157	$ 47,570	$ 47,221	51,157	$ 47,570	$ 53,448
Estimated present value of future obligations and other information
Workers' compensation discount rate			4.22%			2.41%
Other long-term assets
Estimated present value of future obligations and other information
Receivables for traumatic injury claims	$ 4,100			$ 4,100

Represents the change in the liability for workers' compensation due to payments made during the period.

No definition available.

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- Definition

Represents the change in the liability for workers' compensation due to an adjustment for valuation gain or loss.

+ References

No definition available.

+ Details

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- Definition

Represents the change in the liability for workers' compensation due to additional amounts accrued during the period.

+ References

No definition available.

+ Details

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- References

No definition available.

+ Details

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- Definition

Amount recognized for the passage of time, typically for liabilities, that have been discounted to their net present values. Excludes accretion associated with asset retirement obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 420
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- References

No definition available.

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- Definition

Carrying amount due after one year of the balance sheet date (or one operating cycle, if longer) of amount due in settlement of a claim for reimbursement from an insurance company when the Company has suffered a loss covered under an insurance policy.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition

Percent discount applied to worker's compensation reserve liability to reduce the reserve to present value.

+ References

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- Definition

Carrying value as of the balance sheet date of obligations and payables pertaining to claims incurred of a workers compensation nature.

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