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Revenue Recognition (Tables) | 9 Months Ended
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Sep. 30, 2020
Revenue from Contract with Customer [Abstract] |
Disaggregation of Revenue | The following table disaggregates revenue by major sources:
| THREE MONTHS ENDED |  | NINE MONTHS ENDED
| SEPTEMBER 30 |  | SEPTEMBER 30
Major Goods/Service Lines | 2020 |  | 2019 |  | 2020 |  | 2019
Coal Mining | $ | 20,395 |  |  | $ | 18,799 |  |  | $ | 62,896 |  |  | $ | 58,119 |
NAMining | 9,443 |  |  | 8,993 |  |  | 33,115 |  |  | 30,496 |
Minerals Management | 2,722 |  |  | 5,022 |  |  | 9,950 |  |  | 25,950 |
Unallocated Items | 904 |  |  | 52 |  |  | 1,257 |  |  | 726 |
Eliminations | (1,169) |  |  | (263) |  |  | (1,924) |  |  | (1,239) |
Total revenues | $ | 32,295 |  |  | $ | 32,603 |  |  | $ | 105,294 |  |  | $ | 114,052 |
Timing of Revenue Recognition |  |  |  |  |  |  |
Goods transferred at a point in time | $ | 19,871 |  |  | $ | 18,049 |  |  | $ | 61,131 |  |  | $ | 56,012 |
Services transferred over time | 12,424 |  |  | 14,554 |  |  | 44,163 |  |  | 58,040 |
Total revenues | $ | 32,295 |  |  | $ | 32,603 |  |  | $ | 105,294 |  |  | $ | 114,052 |
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, 2020 | $ | 15,444 |  |  | $ | 944 |  |  | $ | 2,153 |
Balance, September 30, 2020 | 16,507 |  |  | 941 |  |  | 1,448 |
Increase (decrease) | $ | 1,063 |  |  | $ | (3) |  |  | $ | (705) |

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- Definition Tabular disclosure of receivable, contract asset, and contract liability from contract with customer. Includes, but is not limited to, change in contract asset and contract liability. + 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=121604090&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=121604090&loc=SL49130545-203045 + Details
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