Note 10 - Derivative Instruments - Summary of Forward Sales Contracts (Details)	12 Months Ended
	Dec. 31, 2021 lb g $ / lb $ / item	Dec. 31, 2020 oz lb $ / lb $ / oz
Silver 2022 Settlements for Provisional Sales [Member]
Ounces/pounds under contract (Pound) | oz		1,282
Average price per ounce/pound (in USD per Pound) | $ / oz		25.00
Gold 2022 Settlements for Provisional Sales [Member]
Ounces/pounds under contract (Pound) | oz		4
Average price per ounce/pound (in USD per Pound) | $ / oz		1,858
Zinc 2022 Settlements for Provisional Sales [Member]
Ounces/pounds under contract (Pound) | lb	13,371	23,314
Average price per ounce/pound (in USD per Pound) | $ / lb	1.39	1.19
Lead 2022 Settlements for Provisional Sales [Member]
Ounces/pounds under contract (Pound) | lb	4,575	4,905
Average price per ounce/pound (in USD per Pound) | $ / lb	0.96	0.90
Zinc 2022 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Pound) | lb	57,706	41,577
Average price per ounce/pound (in USD per Pound) | $ / lb	1.28	1.17
Lead 2022 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Pound) | lb	59,194	30,876
Average price per ounce/pound (in USD per Pound) | $ / lb	0.98	0.88
Zinc 2023 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Pound) | lb	76,280	18,519
Average price per ounce/pound (in USD per Pound) | $ / lb	1.29	1.28
Lead 2023 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Pound) | g	71,650
Average price per ounce/pound (in USD per Pound) | $ / item	1.00