Note 11 - Derivative Instruments (Details Textual) $ in Thousands, MXN in Millions, CAD in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 CAD	Jun. 30, 2017 MXN
Maximum Allocation of Forecasted CAD-demonimated Operating Costs	75.00%		75.00%		75.00%	75.00%
Forecasted CAD-denominated Operating Costs to be Hedged, Term			5 years
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	$ 48		$ 48
Gain (Loss) on Sale of Derivatives	2,487	$ (6)	(5,322)	$ (6)
Gain (Loss) on Components Excluded from Assessment of Foreign Currency Cash Flow Hedge Effectiveness			2
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	3,200		3,200
Derivative, Fair Value, Obligations Under the Agreements	3,200		3,200
Cost of Sales [Member]
Gain (Loss) on Sale of Derivatives			(400)
Other Comprehensive Income (Loss) [Member]
Foreign Currency Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months	400		400
Foreign Exchange Contract [Member] | Other Current Assets [Member]
Derivative Asset, Current	1,100		1,100
Foreign Exchange Contract [Member] | Other Noncurrent Assets [Member]
Derivative Asset, Noncurrent	1,100		1,100
Foreign Exchange Contract [Member] | Other Current Liabilities [Member]
Derivative Liability, Current	400		400
Foreign Exchange Contract [Member] | Other Noncurrent Liabilities [Member]
Derivative Liability, Noncurrent	$ 100		$ 100
Foreign Exchange Contract [Member] | Casa Berardi [Member] | Minimum [Member] | United States of America, Dollars
Derivative, Forward Exchange Rate	1.2787		1.2787		1.2787	1.2787
Foreign Exchange Contract [Member] | Casa Berardi [Member] | Maximum [Member] | United States of America, Dollars
Derivative, Forward Exchange Rate	1.338		1.338		1.338	1.338
Foreign Exchange Contract [Member] | San Sebastian [Member] | Minimum [Member] | United States of America, Dollars
Derivative, Forward Exchange Rate	19.3752		19.3752		19.3752	19.3752
Foreign Exchange Contract [Member] | San Sebastian [Member] | Maximum [Member] | United States of America, Dollars
Derivative, Forward Exchange Rate	21		21		21	21
Foreign Exchange Contract [Member] | Designated as Hedging Instrument [Member] | Casa Berardi [Member]
Derivative, Number of Instruments Held	106		106		106	106
Derivative, Notional Amount	$ 177,000		$ 177,000		CAD 230.1
Foreign Exchange Contract [Member] | Designated as Hedging Instrument [Member] | San Sebastian [Member]
Derivative, Number of Instruments Held	12		12		12	12
Derivative, Notional Amount	$ 4,800		$ 4,800			MXN 96
Commodity Contract [Member] | Other Current Assets [Member]
Derivative Asset, Current	1,200		1,200
Commodity Contract [Member] | Other Current Liabilities [Member]
Derivative Liability, Current	1,300		1,300
Commodity Contract [Member] | Other Noncurrent Liabilities [Member]
Derivative Liability, Noncurrent	$ 100		100
Unsettled Concentrate Sales Contracts [Member]
Derivative, Loss on Derivative			3,300
Forecasted Future Concentrate Contracts [Member]
Derivative, Loss on Derivative			$ 5,300