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Note 11 - Self-Insurance (Details Textual) $ in Thousands | Mar. 31, 2022 USD ($) item | Dec. 31, 2021 USD ($) | Mar. 31, 2021 USD ($)
--- | --- | --- | ---
Restricted Cash and Cash Equivalents, Total | $ 3,288 | $ 3,283 | $ 3,771
Future Workers' Compensation Claim Payments [Member] |  |  |
Restricted Cash and Cash Equivalents, Total | $ 3,300 | 3,300 |
Mining Properties and Mineral Rights [Member] |  |  |
Number of Mining Units | 7 |  |
Area of Real Estate Property | item | 10 |  |
Operating Lease, Liability, Total | $ 262,000 | $ 260,000 |

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