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 9 Months Ended
Sep. 19, 2014
tranch
Mar. 31, 2015
Mar. 31, 2014
Mar. 31, 2015
Segment
Mar. 31, 2014
Jun. 30, 2014
Feb. 18, 2014
Property, Plant and Equipment [Line Items]              
Number of reportable segments       1us-gaap_NumberOfReportableSegments      
Premium on metals position   $ 3,668,000amrk_InventoryPurchasePremiumOnMetalsPositionmarkedtomarket   $ 3,668,000amrk_InventoryPurchasePremiumOnMetalsPositionmarkedtomarket   $ 3,285,000amrk_InventoryPurchasePremiumOnMetalsPositionmarkedtomarket  
Commemorative coin inventory, held at lower of cost or market   65,000amrk_InventoryCommemorativeCoinStatedAtLowerCostOrMarket   65,000amrk_InventoryCommemorativeCoinStatedAtLowerCostOrMarket   2,564,000amrk_InventoryCommemorativeCoinStatedAtLowerCostOrMarket  
Borrowed metals   6,500,000amrk_BorrowedMetals   6,500,000amrk_BorrowedMetals   8,700,000amrk_BorrowedMetals  
Inventories loaned under consignment   5,600,000us-gaap_OtherInventoryMaterialsSuppliesAndMerchandiseUnderConsignment   5,600,000us-gaap_OtherInventoryMaterialsSuppliesAndMerchandiseUnderConsignment   11,100,000us-gaap_OtherInventoryMaterialsSuppliesAndMerchandiseUnderConsignment  
Product under financing arrangement   48,100,000amrk_ProductUnderFinancingArrangement   48,100,000amrk_ProductUnderFinancingArrangement   24,600,000amrk_ProductUnderFinancingArrangement  
Inventory subject to repurchase included in inventory   43,900,000amrk_InventorySubjecttoRepurchaseAgreement   43,900,000amrk_InventorySubjecttoRepurchaseAgreement   27,700,000amrk_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   6,163,000us-gaap_DueFromRelatedParties   6,163,000us-gaap_DueFromRelatedParties   5,852,000us-gaap_DueFromRelatedParties  
Long-term receivable   700,000us-gaap_NotesAndLoansReceivableNetNoncurrent   700,000us-gaap_NotesAndLoansReceivableNetNoncurrent   0us-gaap_NotesAndLoansReceivableNetNoncurrent  
Payables   10,000us-gaap_DueToRelatedPartiesCurrentAndNoncurrent   10,000us-gaap_DueToRelatedPartiesCurrentAndNoncurrent   272,000us-gaap_DueToRelatedPartiesCurrentAndNoncurrent  
Advertising expense   200,000us-gaap_AdvertisingExpense 300,000us-gaap_AdvertisingExpense 500,000us-gaap_AdvertisingExpense 600,000us-gaap_AdvertisingExpense    
Shipping, handling costs   1,500,000us-gaap_ShippingHandlingAndTransportationCosts 1,200,000us-gaap_ShippingHandlingAndTransportationCosts 4,700,000us-gaap_ShippingHandlingAndTransportationCosts 4,200,000us-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            
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
           
Cost-method Investee              
Property, Plant and Equipment [Line Items]              
Receivable   9,900,000us-gaap_DueFromRelatedParties
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
  9,900,000us-gaap_DueFromRelatedParties
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
  2,600,000us-gaap_DueFromRelatedParties
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
 
Secured loans   900,000us-gaap_NotesReceivableNet
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
  900,000us-gaap_NotesReceivableNet
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
  0us-gaap_NotesReceivableNet
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
 
Long-term receivable   700,000us-gaap_NotesAndLoansReceivableNetNoncurrent
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
  700,000us-gaap_NotesAndLoansReceivableNetNoncurrent
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
     
Payables   12,900,000us-gaap_DueToRelatedPartiesCurrentAndNoncurrent
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
  12,900,000us-gaap_DueToRelatedPartiesCurrentAndNoncurrent
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
  3,500,000us-gaap_DueToRelatedPartiesCurrentAndNoncurrent
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
 
Revenue from related party   124,700,000us-gaap_RevenueFromRelatedParties
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
60,200,000us-gaap_RevenueFromRelatedParties
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
352,000,000us-gaap_RevenueFromRelatedParties
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
143,400,000us-gaap_RevenueFromRelatedParties
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
   
Purchases from related party   $ 300,000us-gaap_RelatedPartyTransactionPurchasesFromRelatedParty
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
$ 100,000us-gaap_RelatedPartyTransactionPurchasesFromRelatedParty
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
$ 700,000us-gaap_RelatedPartyTransactionPurchasesFromRelatedParty
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember
$ 2,000,000us-gaap_RelatedPartyTransactionPurchasesFromRelatedParty
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= amrk_CostmethodInvesteeMember