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Note 10 - Self-Insurance (Details Textual) $ in Thousands | Mar. 31, 2023 USD ($) item | Dec. 31, 2022 USD ($) | Mar. 31, 2022 USD ($)
--- | --- | --- | ---
Restricted Cash and Cash Equivalents | $ 3,908 | $ 3,417 | $ 3,288
Future Workers' Compensation Claim Payments [Member] |  |  |
Restricted Cash and Cash Equivalents | $ 3,900 | 3,400 |
Mining Properties and Mineral Rights [Member] |  |  |
Number of Mining Units | 7 |  |
Area of Real Estate Property | item | 10 |  |
Operating Lease, Liability | $ 285,000 | $ 280,000 |

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