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ASSET RETIREMENT OBLIGATIONS (Tables) | 12 Months Ended
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Dec. 31, 2020
ASSET RETIREMENT OBLIGATIONS |
Schedule of activity affecting the asset retirement and mine closing liability | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended December 31, |
​ |  | 2020 |  | 2019 |
​ | ​ | (in thousands) | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Beginning balance | ​ | $ | 137,514 | ​ | $ | 137,114 | ​
Accretion expense | ​ |  | 4,033 | ​ |  | 4,087 | ​
Payments | ​ |  | (1,769) | ​ |  | (2,948) | ​
Allocation of liability associated with acquisitions, mine development and change in assumptions | ​ |  | (11,880) | ​ |  | (739) | ​
Ending balance | ​ | $ | 127,898 | ​ | $ | 137,514 | ​
Schedule of estimated payments of asset retirement obligations | ​
​ | ​ | ​ | ​ | ​
Year Ended | ​ | ​ | ​ | ​
December 31, |  | (in thousands) |
​ | ​ | ​ | ​ | ​
2021 | ​ | $ | 6,411 | ​
2022 | ​ |  | 2,723 | ​
2023 | ​ |  | 2,570 | ​
2024 | ​ |  | 3,317 | ​
2025 | ​ |  | 4,601 | ​
Thereafter | ​ |  | 210,330 | ​
Aggregate undiscounted asset retirement obligations | ​ |  | 229,952 | ​
Effect of discounting | ​ |  | (102,054) | ​
Total asset retirement obligations | ​ |  | 127,898 | ​
Less: current portion | ​ |  | (6,411) | ​
Non-current asset retirement obligations | ​ | $ | 121,487 | ​

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- Definition Tabular disclosure of estimated future payments of asset retirement obligations for each of the five succeeding fiscal years and thereafter. + References No definition available. + Details
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- Definition Tabular disclosure of the changes in carrying amount of a liability for asset retirement obligations, for changes such as new obligations, changes in estimates of existing obligations, spending on existing obligations, property dispositions, and foreign currency translation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13201-110859 + Details
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