Quarterly report pursuant to Section 13 or 15(d)

Inventories (Details)

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Inventories (Details) (USD $)
 6 Months Ended 12 Months Ended
Dec. 31, 2014
Jun. 30, 2014
Inventory Disclosure [Abstract]    
Premium on metals position $ 4,653,000amrk_InventoryPurchasePremiumOnMetalsPositionmarkedtomarket $ 3,285,000amrk_InventoryPurchasePremiumOnMetalsPositionmarkedtomarket
Commemorative coin inventory, held at lower of cost or market 394,000amrk_InventoryCommemorativeCoinStatedAtLowerCostOrMarket 2,564,000amrk_InventoryCommemorativeCoinStatedAtLowerCostOrMarket
Unrealized gains (losses) included in inventory balance (12,300,000)amrk_InventoryUnrealizedGainsLossesResultingFromMarketValueAndCostOfPhysicalInventory 3,800,000amrk_InventoryUnrealizedGainsLossesResultingFromMarketValueAndCostOfPhysicalInventory
Borrowed metals 5,700,000amrk_BorrowedMetals 8,700,000amrk_BorrowedMetals
Product under financing arrangement 80,700,000amrk_ProductUnderFinancingArrangement 24,600,000amrk_ProductUnderFinancingArrangement
Inventories loaned under consignment 4,000,000us-gaap_OtherInventoryMaterialsSuppliesAndMerchandiseUnderConsignment 11,100,000us-gaap_OtherInventoryMaterialsSuppliesAndMerchandiseUnderConsignment
Inventory subject to repurchase included in inventory $ 39,600,000amrk_InventorySubjecttoRepurchaseAgreement $ 24,600,000amrk_InventorySubjecttoRepurchaseAgreement