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