Note 11 - Self-insurance (Details Textual) $ in Thousands	Jun. 30, 2021 USD ($) item	Dec. 31, 2020 USD ($)	Jun. 30, 2020 USD ($)
Restricted Cash and Cash Equivalents, Total	$ 3,495	$ 4,030	$ 4,508
Future Workers' Compensation Claim Payments [Member]
Restricted Cash and Cash Equivalents, Total	$ 3,500	4,000
Mining Properties and Mineral Rights [Member]
Number of Mining Units	7
Area of Real Estate Property \| item	10
Operating Lease, Liability, Total	$ 275,000	$ 269,000

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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-Topic 944
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Name:	us-gaap_RestrictedCashAndCashEquivalents
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant