Note 11 - Self-Insurance (Details Textual) $ in Thousands	Jun. 30, 2022 USD ($) item	Dec. 31, 2021 USD ($)	Jun. 30, 2021 USD ($)
Restricted Cash and Cash Equivalents, Total	$ 3,491	$ 3,283	$ 3,495
Future Workers' Compensation Claim Payments [Member]
Restricted Cash and Cash Equivalents, Total	$ 3,500	3,300
Mining Properties and Mineral Rights [Member]
Number of Mining Units	7
Area of Real Estate Property \| item	10
Operating Lease, Liability, Total	$ 269,000	$ 260,000

Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Name:	us-gaap_RestrictedCashAndCashEquivalents
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant