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Intangible Assets (Tables) | 12 Months Ended
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Dec. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract] |
Schedule of Finite-Lived Intangible Assets | Intangible assets other than goodwill, which are subject to amortization, consist of the following:
| Gross Carrying Amount |  | Accumulated Amortization |  | Net Balance
Balance at December 31, 2019 |  |  |  |  |
Coal supply agreement | $ | 84,200 |  |  | $ | (46,298 | ) |  | $ | 37,902 |
Balance at December 31, 2018 |  |  |  |  |
Coal supply agreement | $ | 84,200 |  |  | $ | (43,684 | ) |  | $ | 40,516 |

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