Note 11 - Summary of Forward Sales Contracts (Details) - 2015 Settlements [Member] oz in Thousands, lb in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016 lb oz $ / lb $ / oz	Dec. 31, 2015 lb oz $ / lb $ / oz
Silver [Member]
Pounds Under Contract | oz	1,196	1,368
Average Price | $ / oz	15.29	14.12
Gold [Member]
Pounds Under Contract | oz	4	5
Average Price | $ / oz	1,225	1,076
Zinc [Member]
Pounds Under Contract | lb	15,818	23,755
Average Price | $ / lb	0.8	0.71
Lead [Member]
Pounds Under Contract | lb	9,700	8,433
Average Price | $ / lb	0.77	0.77