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Gold and Silver Bullion - Bullion Holdings (Details) $ in Thousands | Jun. 30, 2018 USD ($) oz $ / oz | Dec. 31, 2017 USD ($) oz $ / oz
--- | --- | ---
Schedule of Investments [Line Items] |  |
Total carrying value | $ 3,664 | $ 3,812
Gold |  |
Schedule of Investments [Line Items] |  |
Ounces | oz | 1,904 | 1,905
Carrying value per ounce | $ / oz | 1,250 | 1,291
Total carrying value | $ 2,380 | $ 2,459
Silver |  |
Schedule of Investments [Line Items] |  |
Ounces | oz | 80,099 | 80,224
Carrying value per ounce | $ / oz | 16.03 | 16.87
Total carrying value | $ 1,284 | $ 1,353

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