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Note 11 - Derivative Instruments (Details Textual) $ in Thousands, $ in Millions | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Sep. 30, 2019 USD ($) | Sep. 30, 2018 USD ($) | Dec. 31, 2020 USD ($) oz $ / oz | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2020 CAD ($) $ / oz
Maximum Allocation of Forecasted CAD-demonimated Operating Costs |  |  | 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 |  |  | $ 7,600 |  |  |
Foreign Currency Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net |  |  | 2,700 |  |  |
Gain (Loss) on Components Excluded from Assessment of Foreign Currency Cash Flow Hedge Effectiveness |  |  | 0 |  |  |
Derivative, Gain (Loss) on Derivative, Net, Total |  |  | (5,578) | $ (5,613) | $ 15,366 |
Derivative, Gain on Derivative |  |  |  |  | $ 8,100 |
Other Comprehensive Income (Loss) [Member] |  |  |  |  |  |
Foreign Currency Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months |  |  | $ 3,100 |  |  |
Foreign Exchange Contract [Member] | Casa Berardi [Member] | Designated as Hedging Instrument [Member] |  |  |  |  |  |
Derivative, Number of Instruments Held, Total |  |  | 143 |  |  | 143
Derivative, Notional Amount |  |  | $ 223,000 |  |  | $ 293.8
Foreign Exchange Contract [Member] | Casa Berardi [Member] | Designated as Hedging Instrument [Member] | Minimum [Member] |  |  |  |  |  |
Derivative, Forward Exchange Rate |  |  | 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
Silver Contracts [Member] |  |  |  |  |  |
Derivative, Average Price Risk Option Strike Price (in USD per Ounce) | $ / oz |  |  | 16.50 |  |  | 16.50
Derivative, Nonmonetary Notional Amount, Mass (Ounce) | oz |  |  | 1,100,000 |  |  |
Gold Contracts [Member] |  |  |  |  |  |
Derivative, Average Price Risk Option Strike Price (in USD per Ounce) | $ / oz |  |  | 1,650 |  |  | 1,650
Derivative, Nonmonetary Notional Amount, Mass (Ounce) | oz |  |  | 12,992 |  |  |
Unsettled Concentrate Sales Contracts [Member] |  |  |  |  |  |
Derivative, Gain (Loss) on Derivative, Net, Total |  |  | $ (16,400) |  |  |
Forecasted Future Concentrate Contracts [Member] |  |  |  |  |  |
Derivative, Gain (Loss) on Derivative, Net, Total |  |  | (22,100) |  |  |
Derivative, Gain on Derivative | $ 6,700 | $ 32,800 |  |  |  |
Commodity Contract [Member] |  |  |  |  |  |
Derivative Liability, Fair Value, Amount Not Offset Against Collateral, Total |  |  | 12,200 |  |  |
Derivative, Fair Value, Obligations Under the Agreements |  |  | $ 12,200 |  |  |

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