| Standard label: | Prepaid Mineral Royalties, Noncurrent |
| Name: | us-gaap:PrepaidMineralRoyaltiesNoncurrent |
| Documentation: | Carrying amount as of the balance sheet date of capitalized amounts paid for mineral royalties which will be charged against earnings after one year or beyond the normal operating cycle, if longer. |
| Object type: | cm:Concept |
| Data type: | Monetary (xbrli:monetaryItemType) |
| Period type: | As Of (instant) |
| Balance type: | Debit |
| Abstract: | false |
| Workiva Wdesk Taxonomy Analyzer: | us-gaap:PrepaidMineralRoyaltiesNoncurrent |
| Label | Role | Language |
| Prepaid Mineral Royalties, Noncurrent | http://www.xbrl.org/2003/role/label | en-US |
| Reference | Role | Topic |
| FASB Accounting Standards Codification 210 10 S99 1 (SX 210.5-02.17) | http://fasb.org/us-gaap/role/ref/legacyRef | 210 |
| Part Of Roll Up: |
| us-gaap:PrepaidExpenseNoncurrent |