Note 10 - Derivative Instruments - Summary of Forward Sales Contracts (Details) oz in Thousands, lb in Thousands	12 Months Ended
	Dec. 31, 2016 oz $ / oz	Dec. 31, 2015 lb oz $ / oz $ / lb
Silver 2017 Settlements for Provisional Sales [Member]
Ounces/pounds under contract (Ounce) | oz	1,295
Average price per ounce/pound (in USD per Ounce) | $ / oz	16.29
Silver 2016 Settlements for Provisional Sales [Member]
Ounces/pounds under contract (Ounce) | oz		1,368
Average price per ounce/pound (in USD per Ounce) | $ / oz		14.12
Gold 2017 Settlements for Provisional Sales [Member]
Ounces/pounds under contract (Ounce) | oz	4
Average price per ounce/pound (in USD per Ounce) | $ / oz	1,172
Gold 2016 Settlements for Provisional Sales [Member]
Ounces/pounds under contract (Ounce) | oz		5
Average price per ounce/pound (in USD per Ounce) | $ / oz		1,076
Zinc 2017 Settlements for Provisional Sales [Member]
Ounces/pounds under contract (Ounce) | oz	19,070
Average price per ounce/pound (in USD per Ounce) | $ / oz	1.18
Zinc 2016 Settlements for Provisional Sales [Member]
Ounces/pounds under contract (Ounce) | lb		23,755
Average price per ounce/pound (in USD per Ounce) | $ / lb		0.71
Lead 2017 Settlements for Provisional Sales [Member]
Ounces/pounds under contract (Ounce) | oz	7,441
Average price per ounce/pound (in USD per Ounce) | $ / oz	0.97
Lead 2016 Settlements for Provisional Sales [Member]
Ounces/pounds under contract (Ounce) | lb		8,433
Average price per ounce/pound (in USD per Ounce) | $ / lb		0.77
Silver 2017 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | oz
Average price per ounce/pound (in USD per Ounce) | $ / oz
Gold 2017 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | oz
Average price per ounce/pound (in USD per Ounce) | $ / oz
Zinc 2017 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | oz	35,384
Average price per ounce/pound (in USD per Ounce) | $ / oz	1.19
Lead 2017 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | oz	17,637
Average price per ounce/pound (in USD per Ounce) | $ / oz	1.03
Silver 2018 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | oz
Average price per ounce/pound (in USD per Ounce) | $ / oz
Gold 2018 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | oz
Average price per ounce/pound (in USD per Ounce) | $ / oz
Zinc 2018 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | oz	13,779
Average price per ounce/pound (in USD per Ounce) | $ / oz	1.21
Lead 2018 Settlements for Forecasted Sales [Member]
Ounces/pounds under contract (Ounce) | oz	5,732
Average price per ounce/pound (in USD per Ounce) | $ / oz	1.05