Note 11 - Derivative Instruments (Details) - Summary of Forward Sales Contracts lb in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015 $ / oz $ / lb oz lb	Dec. 31, 2014 $ / oz $ / lb oz lb
Silver [Member] | 2015 Settlements [Member]
Contracts on provisional sales
Pounds Under Contract (in Ounces) | oz	1,271	1,607
Average Price Per Pound	14.74	16.06
Average Price Per Ounce	14.74	16.06
Contracts on forecasted sales
Average Price Per Pound
Average Price Per Ounce
Silver [Member] | 2016 Settlements [Member]
Contracts on forecasted sales
Average Price Per Pound
Average Price Per Ounce
Silver [Member] | 2017 Settlements [Member]
Contracts on forecasted sales
Average Price Per Pound
Average Price Per Ounce
Gold [Member] | 2015 Settlements [Member]
Contracts on provisional sales
Pounds Under Contract (in Ounces) | oz	5	6
Average Price Per Pound	1,135	1,195
Average Price Per Ounce	1,135	1,195
Contracts on forecasted sales
Average Price Per Pound
Average Price Per Ounce
Gold [Member] | 2016 Settlements [Member]
Contracts on forecasted sales
Average Price Per Pound
Average Price Per Ounce
Gold [Member] | 2017 Settlements [Member]
Contracts on forecasted sales
Average Price Per Pound
Average Price Per Ounce
Zinc [Member] | 2015 Settlements [Member]
Contracts on provisional sales
Pounds Under Contract (in Pounds) | lb	18,684	19,456
Average Price Per Pound | $ / lb	0.85	1.01
Average Price Per Ounce | $ / lb	0.85	1.01
Contracts on forecasted sales
Pounds Under Contract (in Pounds) | lb		46,738
Average Price Per Pound | $ / lb		0.96
Average Price Per Ounce | $ / lb		0.96
Zinc [Member] | 2016 Settlements [Member]
Contracts on forecasted sales
Pounds Under Contract (in Pounds) | lb		44,699
Average Price Per Pound | $ / lb		0.99
Average Price Per Ounce | $ / lb		0.99
Zinc [Member] | 2017 Settlements [Member]
Contracts on forecasted sales
Pounds Under Contract (in Pounds) | lb		1,984
Average Price Per Pound | $ / lb		1.04
Average Price Per Ounce | $ / lb		1.04
Lead [Member] | 2015 Settlements [Member]
Contracts on provisional sales
Pounds Under Contract (in Pounds) | lb	6,283	8,378
Average Price Per Pound | $ / lb	0.76	0.87
Average Price Per Ounce | $ / lb	0.76	0.87
Contracts on forecasted sales
Pounds Under Contract (in Pounds) | lb		29,652
Average Price Per Pound | $ / lb		1.07
Average Price Per Ounce | $ / lb		1.07
Lead [Member] | 2016 Settlements [Member]
Contracts on forecasted sales
Pounds Under Contract (in Pounds) | lb		34,337
Average Price Per Pound | $ / lb		1.03
Average Price Per Ounce | $ / lb		1.03
Lead [Member] | 2017 Settlements [Member]
Contracts on forecasted sales
Average Price Per Pound | $ / lb
Average Price Per Ounce | $ / lb