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Note 11 - Derivative Instruments (Details Textual) $ in Thousands, $ in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	May 07, 2020 $ / item	Apr. 30, 2020 USD ($) $ / item	Mar. 31, 2020 CAD ($)	Mar. 31, 2020 MXN ($)
Maximum Allocation of Forecasted CAD-demonimated Operating Costs	75.00%				75.00%	75.00%
Forecasted CAD-denominated Operating Costs to be Hedged, Term (Year)	5 years
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax, Ending Balance	$ (19,700)
Foreign Currency Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net	900
Gain (Loss) on Components Excluded from Assessment of Foreign Currency Cash Flow Hedge Effectiveness	0
Derivative, Gain (Loss) on Derivative, Net, Total	10,437	$ (3,686)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral, Total	20,700
Derivative, Fair Value, Obligations Under the Agreements	20,700
Other Comprehensive Income (Loss) [Member]
Foreign Currency Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months	(7,000)
Foreign Exchange Contract [Member] \| Other Current Liabilities [Member]
Derivative Liability, Current	7,500
Foreign Exchange Contract [Member] \| Other Noncurrent Liabilities [Member]
Derivative Liability, Noncurrent	$ 12,000
Foreign Exchange Contract [Member] \| Casa Berardi [Member] \| Designated as Hedging Instrument [Member]
Derivative, Number of Instruments Held, Total	155				155	155
Derivative, Notional Amount	$ 262,900				$ 345
Foreign Exchange Contract [Member] \| Casa Berardi [Member] \| Designated as Hedging Instrument [Member] \| Minimum [Member]
Derivative, Forward Exchange Rate	1.2702				1.2702	1.2702
Foreign Exchange Contract [Member] \| Casa Berardi [Member] \| Designated as Hedging Instrument [Member] \| Maximum [Member]
Derivative, Forward Exchange Rate	1.3785				1.3785	1.3785
Foreign Exchange Contract [Member] \| San Sebastian [Member] \| Designated as Hedging Instrument [Member]
Derivative, Number of Instruments Held, Total	2				2	2
Derivative, Notional Amount	$ 200					$ 3.2
Foreign Exchange Contract [Member] \| San Sebastian [Member] \| Designated as Hedging Instrument [Member] \| Minimum [Member]
Derivative, Forward Exchange Rate	20.8125				20.8125	20.8125
Foreign Exchange Contract [Member] \| San Sebastian [Member] \| Designated as Hedging Instrument [Member] \| Maximum [Member]
Derivative, Forward Exchange Rate	20.8450				20.8450	20.8450
Gold Contracts [Member] \| Subsequent Event [Member]
Derivative, Notional Amount				$ 1,700
Derivative, Average Price Risk Option Strike Price (in USD per Per Share) \| $ / item				1,600
Silver Contracts [Member] \| Subsequent Event [Member]
Derivative, Average Price Risk Option Strike Price (in USD per Per Share) \| $ / item			0
Commodity Contract [Member]
Derivative Liability, Current	$ 100
Derivative Asset, Current	8,800
Derivative Asset, Total	800
Derivative Liability, Total	400
Unsettled Concentrate Sales Contracts [Member]
Derivative, Gain (Loss) on Derivative, Net, Total	1,700
Forecasted Future Concentrate Contracts [Member]
Derivative, Gain (Loss) on Derivative, Net, Total	$ 7,900