Note 10 - Derivative Instruments (Details) - Summary of Forward Sales Contracts lb in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) lb	Dec. 31, 2014 USD ($) lb
2016 Settlements [Member] | Silver [Member]
Contracts on provisional sales
Pounds Under Contract (in Pounds) | lb	1,368
Average Price Per Pound	$ 14.12
Average Price Per Ounce	$ 14.12
Contracts on forecasted sales
Average Price Per Pound
Average Price Per Ounce
2016 Settlements [Member] | Gold [Member]
Contracts on provisional sales
Pounds Under Contract (in Pounds) | lb	5
Average Price Per Pound	$ 1,076
Average Price Per Ounce	$ 1,076
Contracts on forecasted sales
Average Price Per Pound
Average Price Per Ounce
2016 Settlements [Member] | Zinc [Member]
Contracts on provisional sales
Pounds Under Contract (in Pounds) | lb	23,755
Average Price Per Pound	$ 0.71
Average Price Per Ounce	$ 0.71
Contracts on forecasted sales
Pounds Under Contract (in Pounds) | lb		44,699
Average Price Per Pound		$ 0.99
Average Price Per Ounce		$ 0.99
2016 Settlements [Member] | Lead [Member]
Contracts on provisional sales
Pounds Under Contract (in Pounds) | lb	8,433
Average Price Per Pound	$ 0.77
Average Price Per Ounce	$ 0.77
Contracts on forecasted sales
Pounds Under Contract (in Pounds) | lb		34,337
Average Price Per Pound		$ 1.03
Average Price Per Ounce		$ 1.03
2015 Settlements [Member] | Silver [Member]
Contracts on provisional sales
Pounds Under Contract (in Pounds) | lb		1,607
Average Price Per Pound		$ 16.06
Average Price Per Ounce		$ 16.06
Contracts on forecasted sales
Average Price Per Pound
Average Price Per Ounce
2015 Settlements [Member] | Gold [Member]
Contracts on provisional sales
Pounds Under Contract (in Pounds) | lb		6
Average Price Per Pound		$ 1,195
Average Price Per Ounce		$ 1,195
Contracts on forecasted sales
Average Price Per Pound
Average Price Per Ounce
2015 Settlements [Member] | Zinc [Member]
Contracts on provisional sales
Pounds Under Contract (in Pounds) | lb		19,456
Average Price Per Pound		$ 1.01
Average Price Per Ounce		$ 1.01
Contracts on forecasted sales
Pounds Under Contract (in Pounds) | lb		46,738
Average Price Per Pound		$ 0.96
Average Price Per Ounce		$ 0.96
2015 Settlements [Member] | Lead [Member]
Contracts on provisional sales
Pounds Under Contract (in Pounds) | lb		8,378
Average Price Per Pound		$ 0.87
Average Price Per Ounce		$ 0.87
Contracts on forecasted sales
Pounds Under Contract (in Pounds) | lb		29,652
Average Price Per Pound		$ 1.07
Average Price Per Ounce		$ 1.07
2017 Settlements [Member] | Silver [Member]
Contracts on forecasted sales
Average Price Per Pound
Average Price Per Ounce
2017 Settlements [Member] | Gold [Member]
Contracts on forecasted sales
Average Price Per Pound
Average Price Per Ounce
2017 Settlements [Member] | Zinc [Member]
Contracts on forecasted sales
Pounds Under Contract (in Pounds) | lb		1,984
Average Price Per Pound		$ 1.04
Average Price Per Ounce		$ 1.04
2017 Settlements [Member] | Lead [Member]
Contracts on forecasted sales
Pounds Under Contract (in Pounds) | lb
Average Price Per Pound
Average Price Per Ounce