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Fair Value Measurements (Tables) | 9 Months Ended
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Sep. 30, 2025
Fair Value Disclosures [Abstract] |
Schedule of fair value measurements hierarchy | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | Fair Value | ​
​ |  | Carrying Value |  | Level 1 |  | Level 2 |  | Level 3 |
​ | ​ | (in thousands) | ​
September 30, 2025 | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Recorded on a recurring basis: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Digital assets | ​ | $ | 64,809 | ​ | $ | 64,809 | ​ | $ | — | ​ | $ | — | ​
Contingent consideration | ​ | $ | 13,592 | ​ | $ | — | ​ | $ | — | ​ | $ | 13,592 | ​
Debt securities | ​ | $ | 13,193 | ​ | $ | — | ​ | $ | — | ​ | $ | 13,193 | ​
Additional disclosures: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Long-term debt | ​ | $ | 470,289 | ​ | $ | — | ​ | $ | 506,676 | ​ | $ | — | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
December 31, 2024 | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Recorded on a recurring basis: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Digital assets | ​ | $ | 45,037 | ​ | $ | 45,037 | ​ | $ | — | ​ | $ | — | ​
Contingent consideration | ​ | $ | 13,100 | ​ | $ | — | ​ | $ | — | ​ | $ | 13,100 | ​
Additional disclosures: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Long-term debt | ​ | $ | 490,387 | ​ | $ | — | ​ | $ | 523,461 | ​ | $ | — | ​
Schedule of fair value measurements inputs | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Valuation Technique(s) |  | Unobservable Input |  | Range/Amount (Average) (a) | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
September 30, 2025 | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Contingent Consideration | ​ | Option approach methodology simulation | ​ | Cost of Debt | ​ | 6.51% - 8.56% | ​
​ | ​ | ​ | ​ | Coal price volatility | ​ | 6.2% | ​
​ | ​ | ​ | ​ | Market price of risk adjustment (annual) | ​ | 6.2% | ​
December 31, 2024 | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Contingent Consideration | ​ | Option approach methodology simulation | ​ | Cost of Debt | ​ | 6.51% - 8.56% | ​
​ | ​ | ​ | ​ | Coal price volatility | ​ | 6.2% | ​
​ | ​ | ​ | ​ | Market price of risk adjustment (annual) | ​ | 6.2% | ​
| (a) | Averages represent the arithmetic average of the inputs and is not weighted by a relative fair value or notional amount.
​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Valuation Technique(s) |  | Unobservable Input |  | Range/Amount (Average) (a) | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
September 30, 2025 | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Debt securities | ​ | Option-pricing approach methodology | ​ | Industry volatility | ​ | 38.1% – 64.8% (48.0%) | ​
​ | ​ | ​ | ​ | Estimated time to exit | ​ | 1.75 - 3.75 (2.75) years | ​
​ | ​ | Income approach methodology | ​ | Forecasted future cash flow | ​ | $906.6 - $1,285.9 ($1,096.3) million | ​
​ | ​ | ​ | ​ | Cost of capital | ​ | 14.67% - 19.51% (16.58%) | ​
| (a) | Averages represent the arithmetic average of the inputs and is not weighted by a relative fair value or notional amount.
​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Valuation Technique(s) |  | Unobservable Input |  | Range/Amount (Average) (a) | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Common Stock | ​ | Option-pricing approach methodology | ​ | Industry volatility | ​ | 29.10% - 70.86% (49.98%) | ​
​ | ​ | ​ | ​ | Estimated time to exit | ​ | 2.0 - 4.0 (3.0) years | ​
​ | ​ | Income approach methodology | ​ | Forecasted future cash flow | ​ | $906.6 - $1,285.9 ($1,096.3) million | ​
​ | ​ | ​ | ​ | Cost of capital | ​ | 11.25% - 16.58% (13.92%) | ​
| (a) | Averages represent the arithmetic average of the inputs and is not weighted by a relative fair value or notional amount.
​
Schedule of changes in our contingent consideration liability | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Three Months Ended | ​ | Nine Months Ended | ​
​ | ​ | September 30, | ​ | September 30, | ​
​ |  | 2025 |  | 2024 |  | 2025 | ​ | 2024 |
​ | ​ | (in thousands) | ​
Beginning balance | ​ | $ | 10,677 | ​ | $ | 6,089 | ​ | $ | 13,100 | ​ | $ | 9,900 | ​
Noncash changes in fair value (1) | ​ | ​ | 4,359 | ​ | ​ | — | ​ | ​ | 6,364 | ​ | ​ | — | ​
Payments | ​ | ​ | (1,444) | ​ | ​ | (1,637) | ​ | ​ | (5,872) | ​ | ​ | (5,448) | ​
Ending balance | ​ | $ | 13,592 | ​ | $ | 4,452 | ​ | $ | 13,592 | ​ | $ | 4,452 | ​
| (1) | Noncash changes in the fair value of our continent consideration liability are included in the Operating expenses (excluding depreciation, depletion and amortization) line item within our condensed consolidated statements of income.
Schedule of changes in our debt securities | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Three Months Ended | ​ | Nine Months Ended | ​
​ | ​ | September 30, | ​ | September 30, | ​
​ |  | 2025 |  | 2025 |
​ | ​ | (in thousands) | ​
Beginning balance | ​ | $ | 13,046 | ​ | $ | — | ​
Noncash changes in fair value (1) | ​ | ​ | (685) | ​ | ​ | 10,234 | ​
Payments | ​ | ​ | 832 | ​ | ​ | 2,959 | ​
Ending balance | ​ | $ | 13,193 | ​ | $ | 13,193 | ​
| (1) | Noncash changes in the fair value of our debt securities are included in the Change in unrealized gains (losses) on debt securities line item within our condensed consolidated statements of comprehensive income.

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- Definition Tabular disclosure of input and valuation technique used to measure fair value and change in valuation approach and technique for each separate class of asset and liability measured on recurring and nonrecurring basis. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 103 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482078/820-10-55-103 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (bbb)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (bbb)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 + Details
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- Definition Tabular disclosure of the fair value measurement of assets using significant unobservable inputs (Level 3), a reconciliation of the beginning and ending balances, separately presenting changes during the period attributable to the following: (1) total gains or losses for the period (realized and unrealized), segregating those gains or losses included in earnings (or changes in net assets) and gains or losses recognized in other comprehensive income (loss), and a description of where those gains or losses included in earnings (or changes in net assets) are reported in the statement of income (or activities); (2) purchases, sales, issues, and settlements (each type disclosed separately); and (3) transfers in and transfers out of Level 3 (for example, transfers due to changes in the observability of significant inputs), by class of asset. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 101 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482078/820-10-55-101 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-3 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 + Details
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- Definition Tabular disclosure of the fair value of financial instruments, including financial assets and financial liabilities, and the measurements of those instruments, assets, and liabilities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 11 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482907/825-10-50-11 + Details
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- Definition Tabular disclosure of contingent payment arrangements including the terms that will result in payment and the accounting treatment that will be followed if such contingencies occur, including the potential impact on earnings per share if contingencies are to be settled in common stock of the entity. The description also may include the period over which amounts are expected to be paid, and changes in the amount since the previous reporting period. This also includes contingent options and commitments. + References No definition available. + Details
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