Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies (Narrative) (Details)

v2.4.1.9
Summary of Significant Accounting Policies (Narrative) (Details) (USD $)
0 Months Ended 3 Months Ended 6 Months Ended
Sep. 19, 2014
tranch
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2014
Segment
Dec. 31, 2013
Sep. 25, 2014
Jun. 30, 2014
Feb. 18, 2014
Property, Plant and Equipment [Line Items]                
Number of reportable segments       1us-gaap_NumberOfReportableSegments        
Premium on metals position   $ 4,653,000amrk_InventoryPurchasePremiumOnMetalsPositionmarkedtomarket   $ 4,653,000amrk_InventoryPurchasePremiumOnMetalsPositionmarkedtomarket     $ 3,285,000amrk_InventoryPurchasePremiumOnMetalsPositionmarkedtomarket  
Commemorative coin inventory, held at lower of cost or market   394,000amrk_InventoryCommemorativeCoinStatedAtLowerCostOrMarket   394,000amrk_InventoryCommemorativeCoinStatedAtLowerCostOrMarket     2,564,000amrk_InventoryCommemorativeCoinStatedAtLowerCostOrMarket  
Borrowed metals   5,700,000amrk_BorrowedMetals   5,700,000amrk_BorrowedMetals     8,700,000amrk_BorrowedMetals  
Inventories loaned under consignment   4,000,000us-gaap_OtherInventoryMaterialsSuppliesAndMerchandiseUnderConsignment   4,000,000us-gaap_OtherInventoryMaterialsSuppliesAndMerchandiseUnderConsignment     11,100,000us-gaap_OtherInventoryMaterialsSuppliesAndMerchandiseUnderConsignment  
Product under financing arrangement   80,700,000amrk_ProductUnderFinancingArrangement   80,700,000amrk_ProductUnderFinancingArrangement     24,600,000amrk_ProductUnderFinancingArrangement  
Inventory subject to repurchase included in inventory   39,600,000amrk_InventorySubjecttoRepurchaseAgreement   39,600,000amrk_InventorySubjecttoRepurchaseAgreement     24,600,000amrk_InventorySubjecttoRepurchaseAgreement  
Ownership percentage               2.50%amrk_Noncontrollingownershippercentagecostmethodinvestment
Long-term investments   1,611,000us-gaap_CostMethodInvestments   1,611,000us-gaap_CostMethodInvestments     500,000us-gaap_CostMethodInvestments 500,000us-gaap_CostMethodInvestments
Receivable   8,539,000us-gaap_DueFromRelatedParties   8,539,000us-gaap_DueFromRelatedParties     5,852,000us-gaap_DueFromRelatedParties  
Long-term receivables   800,000us-gaap_NotesAndLoansReceivableNetNoncurrent   800,000us-gaap_NotesAndLoansReceivableNetNoncurrent     0us-gaap_NotesAndLoansReceivableNetNoncurrent  
Payables   17,000us-gaap_DueToRelatedPartiesCurrentAndNoncurrent   17,000us-gaap_DueToRelatedPartiesCurrentAndNoncurrent     272,000us-gaap_DueToRelatedPartiesCurrentAndNoncurrent  
Advertising expense   100,000us-gaap_AdvertisingExpense 200,000us-gaap_AdvertisingExpense 300,000us-gaap_AdvertisingExpense 300,000us-gaap_AdvertisingExpense      
Shipping, handling costs   1,800,000us-gaap_ShippingHandlingAndTransportationCosts 1,300,000us-gaap_ShippingHandlingAndTransportationCosts 3,200,000us-gaap_ShippingHandlingAndTransportationCosts 3,000,000us-gaap_ShippingHandlingAndTransportationCosts      
Number of tranches 2amrk_NoncontrollingInterestAgreementtoPurchaseCommonStockNumberofTranches              
Payment for closing of Tranche A 2,000,000us-gaap_PaymentsToAcquireBusinessesAndInterestInAffiliates              
Payments to acquire Tranche A 1,100,000amrk_PaymentstoAcquireBusinessesandInterestinAffiliatesTranceOne              
Payable on closing of Tranche B           900,000amrk_CostMethodInvestmentRemainingInvestmentObligation    
Exclusive supplier agreement, period, Tranche A 5 years              
Exclusive supplier agreement, period 3 years              
Minimum                
Property, Plant and Equipment [Line Items]                
Estimated useful lives of related assets       3 years        
Estimated useful lives of intangibles       4 years        
Maximum                
Property, Plant and Equipment [Line Items]                
Estimated useful lives of related assets       5 years        
Estimated useful lives of intangibles       15 years        
Common Class A                
Property, Plant and Equipment [Line Items]                
Agreement to purchase noncontrolling interest, percentage 9.00%amrk_CostMethodInvestmentAgreementtoPurchaseCommonStockPercentage
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
             
Percentage of stock to be purchased for Tranche A 5.00%amrk_CostMethodInvestmentAgreementtoPurchaseCommonStockFirstTranchePercentage
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
             
Percentage of stock to be purchased for Tranche B 4.00%amrk_CostMethodInvestmentAgreementtoPurchaseCommonStockSecondTranchePercentage
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
             
Cost-method Investee                
Property, Plant and Equipment [Line Items]                
Receivable   18,300,000us-gaap_DueFromRelatedParties
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
  18,300,000us-gaap_DueFromRelatedParties
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
    2,600,000us-gaap_DueFromRelatedParties
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
 
Secured loans   1,000,000us-gaap_NotesReceivableNet
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
  1,000,000us-gaap_NotesReceivableNet
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
    0us-gaap_NotesReceivableNet
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
 
Long-term receivables   800,000us-gaap_NotesAndLoansReceivableNetNoncurrent
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
  800,000us-gaap_NotesAndLoansReceivableNetNoncurrent
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
       
Payables   26,100,000us-gaap_DueToRelatedPartiesCurrentAndNoncurrent
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
  26,100,000us-gaap_DueToRelatedPartiesCurrentAndNoncurrent
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
    3,500,000us-gaap_DueToRelatedPartiesCurrentAndNoncurrent
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
 
Revenue from related party   139,400,000us-gaap_RevenueFromRelatedParties
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
46,900,000us-gaap_RevenueFromRelatedParties
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
227,400,000us-gaap_RevenueFromRelatedParties
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
83,200,000us-gaap_RevenueFromRelatedParties
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
     
Purchases from related party   $ 0us-gaap_RelatedPartyTransactionPurchasesFromRelatedParty
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
$ 1,900,000us-gaap_RelatedPartyTransactionPurchasesFromRelatedParty
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
$ 400,000us-gaap_RelatedPartyTransactionPurchasesFromRelatedParty
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
$ 1,900,000us-gaap_RelatedPartyTransactionPurchasesFromRelatedParty
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember