Note 8 - Derivative Instruments - Summary of Forward Sales Contracts (Details) oz in Thousands, lb in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2022 oz lb $ / oz $ / lb $ / item	Dec. 31, 2021 oz lb $ / oz $ / lb $ / item
Silver 2022 Settlements for Provisional Sales [Member]
Ounces/pounds under contract (Ounce) | oz	1,573	1,814
Average price per ounce/pound (in USD per Ounce) | $ / oz	24.73	23.02
Gold 2022 Settlements for Provisional Sales [Member]
Ounces/pounds under contract (Ounce) | oz	5	6
Average price per ounce/pound (in USD per Ounce) | $ / oz	1,912	1,812
Zinc 2022 Settlements for Provisional Sales [Member]
Ounces/pounds under contract (Ounce) | lb	16,976	13,371
Average price per ounce/pound (in USD per Ounce) | $ / lb	1.27	1.39
Lead 2022 Settlements for Provisional Sales [Member]
Ounces/pounds under contract (Ounce) | lb	5,732	4,575
Average price per ounce/pound (in USD per Ounce) | $ / lb	0.97	0.96
Silver 2022 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | oz	0	0
Gold 2022 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | oz	0	0
Zinc 2022 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | lb	37,644	57,706
Average price per ounce/pound (in USD per Ounce) | $ / lb	1.31	1.28
Lead 2022 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | lb	46,517	59,194
Average price per ounce/pound (in USD per Ounce) | $ / lb	0.98	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	78,264	76,280
Average price per ounce/pound (in USD per Ounce) | $ / lb	1.30	1.29
Lead 2023 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | lb	75,618	71,650
Average price per ounce/pound (in USD per Ounce) | $ / item	1.00	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	64,650
Average price per ounce/pound (in USD per Ounce) | $ / item	1.32
Lead 2024 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | lb	23,149
Average price per ounce/pound (in USD per Ounce) | $ / item	1.01