Note 8 - Derivative Instruments - Summary of Forward Sales Contracts (Details) oz in Thousands, lb in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2022 oz lb $ / oz $ / lb $ / item	Dec. 31, 2021 oz lb $ / oz $ / lb $ / item
Silver 2021 Settlements for Provisional Sales [Member]
Ounces/pounds under contract (Ounce) | oz	1,729
Average price per ounce/pound (in USD per Ounce) | $ / oz	22.19
Silver 2022 Settlements for Provisional Sales [Member]
Ounces/pounds under contract (Ounce) | oz		1,814
Average price per ounce/pound (in USD per Ounce) | $ / oz		23.02
Gold 2021 Settlements for Provisional Sales [Member]
Ounces/pounds under contract (Ounce) | oz	3
Average price per ounce/pound (in USD per Ounce) | $ / oz	1,836
Gold 2022 Settlements for Provisional Sales [Member]
Ounces/pounds under contract (Ounce) | oz		6
Average price per ounce/pound (in USD per Ounce) | $ / oz		1,812
Zinc 2021 Settlements for Provisional Sales [Member]
Ounces/pounds under contract (Ounce) | lb	6,504
Average price per ounce/pound (in USD per Ounce) | $ / lb	1.58
Zinc 2022 Settlements for Provisional Sales [Member]
Ounces/pounds under contract (Ounce) | lb		13,371
Average price per ounce/pound (in USD per Ounce) | $ / lb		1.39
Lead 2021 Settlements for Provisional Sales [Member]
Ounces/pounds under contract (Ounce) | lb	3,638
Average price per ounce/pound (in USD per Ounce) | $ / lb	0.90
Lead 2022 Settlements for Provisional Sales [Member]
Ounces/pounds under contract (Ounce) | lb		4,575
Average price per ounce/pound (in USD per Ounce) | $ / lb		0.96
Silver 2021 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | oz	0
Silver 2022 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | oz	0	0
Gold 2021 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | oz	0
Gold 2022 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | oz	0	0
Zinc 2021 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | lb	38,030
Average price per ounce/pound (in USD per Ounce) | $ / lb	1.31
Zinc 2022 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | lb	78,264	57,706
Average price per ounce/pound (in USD per Ounce) | $ / lb	1.30	1.28
Lead 2021 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | lb	34,778
Average price per ounce/pound (in USD per Ounce) | $ / lb	0.98
Lead 2022 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | lb	75,618	59,194
Average price per ounce/pound (in USD per Ounce)	1.00	0.98
Silver 2023 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | oz	0	0
Gold 2023 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | oz	0	0
Zinc 2023 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | lb	78,760	76,280
Average price per ounce/pound (in USD per Ounce)	1.34	1.29
Lead 2023 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | lb	31,526	71,650
Average price per ounce/pound (in USD per Ounce) | $ / item	1.01	1.00
Silver 2024 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | oz	0
Gold 2024 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | oz	0
Zinc 2024 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | lb	1,157
Average price per ounce/pound (in USD per Ounce) | $ / item	1.37
Lead 2024 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | lb	0