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Revenue Recognition (Tables) | 6 Months Ended
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Jun. 30, 2020
Revenue from Contract with Customer [Abstract] |
Disaggregation of Revenue | The following table disaggregates revenue by major sources:
| THREE MONTHS ENDED |  | SIX MONTHS ENDED
| JUNE 30 |  | JUNE 30
Major Goods/Service Lines | 2020 |  | 2019 |  | 2020 |  | 2019
Coal Mining | $ | 21,573 |  |  | $ | 22,570 |  |  | $ | 42,501 |  |  | $ | 39,320 |
NAMining | 12,048 |  |  | 10,728 |  |  | 23,672 |  |  | 21,503 |
Minerals Management | 1,987 |  |  | 8,242 |  |  | 7,228 |  |  | 20,928 |
Unallocated Items | 327 |  |  | 131 |  |  | 353 |  |  | 674 |
Eliminations | (580 | ) |  | (319 | ) |  | (755 | ) |  | (976 | )
Total revenues | $ | 35,355 |  |  | $ | 41,352 |  |  | $ | 72,999 |  |  | $ | 81,449 |
Timing of Revenue Recognition |  |  |  |  |  |  |
Goods transferred at a point in time | $ | 20,976 |  |  | $ | 21,879 |  |  | $ | 41,260 |  |  | $ | 37,964 |
Services transferred over time | 14,379 |  |  | 19,473 |  |  | 31,739 |  |  | 43,485 |
Total revenues | $ | 35,355 |  |  | $ | 41,352 |  |  | $ | 72,999 |  |  | $ | 81,449 |
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, June 30, 2020 | 20,335 |  |  | 941 |  |  | 1,683 |
Increase (decrease) | $ | 4,891 |  |  | $ | (3 | ) |  | $ | (470 | )

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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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- References No definition available. + Details
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