Note 11 - Derivative Instruments (Details Textual) $ in Thousands, MXN in Millions, CAD in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 CAD	Sep. 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	$ 6,800		$ 6,800
Gain (Loss) on Sale of Derivatives	(11,226)	$ 7	(16,548)
Gain (Loss) on Components Excluded from Assessment of Foreign Currency Cash Flow Hedge Effectiveness			2
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	14,400		14,400
Derivative, Fair Value, Obligations Under the Agreements	14,400		14,400
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	2,900		2,900
Foreign Exchange Contract [Member] | Other Current Assets [Member]
Derivative Asset, Current	2,800		2,800
Foreign Exchange Contract [Member] | Other Noncurrent Liabilities [Member]
Derivative Asset, Noncurrent	$ 3,700		$ 3,700
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	19.591		19.591		19.591	19.591
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	94		94		94	94
Derivative, Notional Amount	$ 154,000		$ 154,000		CAD 200.1
Foreign Exchange Contract [Member] | Designated as Hedging Instrument [Member] | San Sebastian [Member]
Derivative, Number of Instruments Held	6		6		6	6
Derivative, Notional Amount	$ 2,200		$ 2,200			MXN 43.3
Commodity Contract [Member] | Other Current Assets [Member]
Derivative Asset, Current	400		400
Derivative Asset, Fair Value, Gross Liability	100		100
Commodity Contract [Member] | Other Noncurrent Liabilities [Member]
Derivative Liability, Noncurrent	4,000		4,000
Commodity Contract [Member] | Other Current Liabilities [Member]
Derivative Liability, Current	7,900		7,900
Derivative Liability, Fair Value, Gross Asset	$ 200		200
Unsettled Concentrate Sales Contracts [Member]
Derivative, Loss on Derivative			3,900
Forecasted Future Concentrate Contracts [Member]
Derivative, Loss on Derivative			$ 16,500