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Note 2 - Revision of Previously Issued Financial Statements for Immaterial Misstatements (Details Textual) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended | 9 Months Ended | 12 Months Ended
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Sep. 30, 2021 | Mar. 31, 2021 | Mar. 31, 2020 | Jun. 30, 2021 | Jun. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Depreciation, Depletion and Amortization, Total |  | $ 46,957 | $ 39,779 | $ 92,861 | $ 79,598 | $ 139,800 | $ 120,076 | $ 155,006 | $ 196,408 | $ 138,681
Revision of Prior Period, Adjustment [Member] |  |  |  |  |  |  |  |  |  |
Depreciation, Depletion and Amortization, Total |  | $ (2,589) | $ (1,851) | $ (5,260) | $ (4,587) |  | $ (6,835) | $ (9,020) | $ (8,067) | $ (2,224)
Revision of Prior Period, Adjustment [Member] | Hecla Quebec. Inc [Member] |  |  |  |  |  |  |  |  |  |
Depreciation, Depletion and Amortization, Total | $ 38,200 |  |  |  |  |  |  |  |  |

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