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Revenue Recognition (Tables) | 12 Months Ended
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Dec. 31, 2019
Revenue from Contract with Customer [Abstract] |
Disaggregation of Revenue | The following table disaggregates revenue by major sources for the years ended December 31:
Major Goods/Service Lines | 2019 |  | 2018
Coal Mining | $ | 68,701 |  |  | $ | 81,549 |
NAMining | 42,823 |  |  | 36,950 |
Minerals Management | 30,119 |  |  | 17,352 |
Unallocated Items | 790 |  |  | 665 |
Eliminations | (1,443 | ) |  | (1,141 | )
Total revenues | $ | 140,990 |  |  | $ | 135,375 |
Timing of Revenue Recognition |  |  |
Goods transferred at a point in time | $ | 66,102 |  |  | $ | 78,849 |
Services transferred over time | 74,888 |  |  | 56,526 |
Total revenues | $ | 140,990 |  |  | $ | 135,375 |
Contract Balances | The opening and closing balances of the Company’s current and long-term contract liabilities and receivables are as follows:
| Contract balances
| Trade accounts receivable, net |  | Contract liability (current) |  | Contract liability (long-term)
Balance, January 1, 2019 | $ | 20,817 |  |  | $ | 754 |  |  | $ | 2,008 |
Balance, December 31, 2019 | 15,444 |  |  | 944 |  |  | 2,153 |
Increase (decrease) | $ | (5,373 | ) |  | $ | 190 |  |  | $ | 145 |

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- Definition Tabular disclosure of contract balances and changes in contract balances. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130551-203045 + Details
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- Definition Tabular disclosure of disaggregation of revenue into categories depicting how nature, amount, timing, and uncertainty of revenue and cash flows are affected by economic factor. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130545-203045 + Details
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