Note 2 - Long-lived Asset Impairments (Details Textual) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended	12 Months Ended
	Aug. 31, 2020	Dec. 31, 2019	Sep. 30, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Asset Impairment Charges, Total				$ 1,588	$ 1,799
Prosperity Mine [Member]
Asset Impairment Charges, Total				1,600
Mineral Properties, Scrap Value				1,100
Mineral Properties, Net, Total				2,700
Hourglass Sands [Member]
Asset Impairment Charges, Total	$ 1,800	$ 2,900	$ 1,800			$ 2,900
Mineral Properties, Net, Total		$ 1,900				$ 1,900
COVID-19 Pandemic [Member]
Asset Impairment Charges, Total				$ 0	$ 0