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Fair Value Measurement - Realized Unrealized Derivatives, net (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020
Derivatives, Fair Value [Line Items] |  |  |  |
Realized (loss) gain | $ (246) | $ 653 | $ 204 | $ 250
Unrealized (loss) gain | (232) | (103) | (48) | (232)
Total realized/ unrealized derivatives, net | (478) | 550 | 156 | 18
Gold |  |  |  |
Derivatives, Fair Value [Line Items] |  |  |  |
Realized (loss) gain | (110) | 132 | (133) | 651
Unrealized (loss) gain | 28 | (11) | 58 | (209)
Total realized/ unrealized derivatives, net | (82) | 121 | (75) | 442
Silver |  |  |  |
Derivatives, Fair Value [Line Items] |  |  |  |
Realized (loss) gain | (295) | 339 | (123) | 451
Unrealized (loss) gain | (11) | (47) | 10 | (290)
Total realized/ unrealized derivatives, net | (306) | 292 | (113) | 161
Copper |  |  |  |
Derivatives, Fair Value [Line Items] |  |  |  |
Realized (loss) gain | (4) | 89 | 63 | 20
Unrealized (loss) gain | (16) | (24) | (24) | (9)
Total realized/ unrealized derivatives, net | (20) | 65 | 39 | 11
Lead |  |  |  |
Derivatives, Fair Value [Line Items] |  |  |  |
Realized (loss) gain | 72 | 16 | 146 | (143)
Unrealized (loss) gain | (84) | (10) | (63) | 41
Total realized/ unrealized derivatives, net | (12) | 6 | 83 | (102)
Zinc |  |  |  |
Derivatives, Fair Value [Line Items] |  |  |  |
Realized (loss) gain | 91 | 77 | 251 | (729)
Unrealized (loss) gain | (149) | (11) | (29) | 235
Total realized/ unrealized derivatives, net | $ (58) | $ 66 | $ 222 | $ (494)

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Net Increase or Decrease in the fair value of the embedded derivative or group of embedded derivatives included in earnings in the period. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 15 -URI http://asc.fasb.org/subtopic&trid=2229187 + Details
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- Definition The difference between the book value and the sale price of options, swaps, futures, forward contracts, and other derivative instruments. This element refers to the gain (loss) included in earnings. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.13(h)) -URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260 + Details
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- Definition The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585 + Details
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