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Investments (Tables) | 9 Months Ended
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Sep. 30, 2025
Investments [Abstract] |
Schedule of changes in equity method investments | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Three Months Ended | ​ | Nine Months Ended | ​
​ | ​ | September 30, | ​ | September 30, | ​
​ |  | 2025 |  | 2024 |  | 2025 |  | 2024 |
​ | ​ | (in thousands) | ​
Beginning balance | ​ | $ | 29,628 | ​ | $ | 45,088 | ​ | $ | 35,532 | ​ | $ | 46,503 | ​
Contributions | ​ | ​ | 22,874 | ​ | ​ | 108 | ​ | ​ | 24,265 | ​ | ​ | 1,398 | ​
Net income (loss) on equity method investments | ​ | ​ | 4,487 | ​ | ​ | (2,327) | ​ | ​ | 945 | ​ | ​ | (3,032) | ​
Distributions received | ​ | ​ | (2,407) | ​ | ​ | (849) | ​ | ​ | (6,160) | ​ | ​ | (2,849) | ​
Change in our share of net assets | ​ | ​ | — | ​ | ​ | (5,118) | ​ | ​ | — | ​ | ​ | (5,118) | ​
Ending balance | ​ | $ | 54,582 | ​ | $ | 36,902 | ​ | $ | 54,582 | ​ | $ | 36,902 | ​
Schedule of debt securities holdings |
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | September 30, 2025 | ​
​ | ​ | Cost Basis | ​ | Unrealized Gains (1) | ​ | Fair Value | ​
​ | ​ | (in thousands) | ​
Debt Securities | ​ | $ | 2,959 | ​ | $ | 10,234 | ​ | $ | 13,193 | ​
(1) | Unrealized gains in 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.
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.
​

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