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           Receivables (Narrative) (Details) (USD $)
  
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        6 Months Ended | 
        0 Months Ended | 
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           Dec. 31, 2014
 
          class
 
          loan 
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           Dec. 31, 2013 
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           Sep. 27, 2013 
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           Jul. 02, 2014 
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           Jun. 30, 2014
 
          loan 
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           Jun. 18, 2014 
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           Jun. 05, 2014 
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           Oct. 09, 2014 
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           Jan. 23, 2015 
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        | Accounts, Notes, Loans and Financing Receivable [Line Items] | 
         
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        | Loans receivable average effective rate of interest (percentage) | 
        
8.30%amrk_LoansReceivableAverageEffectiveRateOfInterest
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7.90%amrk_LoansReceivableAverageEffectiveRateOfInterest
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        | Short term loan receivable | 
         
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$ 3,700,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
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$ 2,600,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
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$ 3,800,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
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        | Option to extend maturity | 
        180 days
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        | Classes of receivables | 
        
3amrk_ClassesOfReceivables
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        | Loans receivable payment terms for interest | 
        30 days
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        | Delinquent period | 
        30 days
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        | Loan receivable liquidation period post default | 
        90 days
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        | Number of loans | 
        
2amrk_FinanceReceivableNumberofLoans
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0amrk_FinanceReceivableNumberofLoans
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        | Minimum | 
         
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        | Accounts, Notes, Loans and Financing Receivable [Line Items] | 
         
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        | Credit quality indicator Loan-to-value threshold percentage | 
        
75.00%amrk_CreditQualityIndicatorLoanToValueThresholdPercentage / us-gaap_RangeAxis = us-gaap_MinimumMember
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        | Maximum | 
         
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        | Accounts, Notes, Loans and Financing Receivable [Line Items] | 
         
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        | Secured loans-to-value percentage | 
        
100.00%amrk_SecuredLoansToValuePercentage / us-gaap_RangeAxis = us-gaap_MaximumMember
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        | Collateral Finance Corporation | 
         
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        | Accounts, Notes, Loans and Financing Receivable [Line Items] | 
         
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        | Short term loan receivable | 
        
3,000,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / dei_LegalEntityAxis = amrk_CollateralFinanceCorporationMember
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12,800,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / dei_LegalEntityAxis = amrk_CollateralFinanceCorporationMember
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        | Payments to acquire loans receivable | 
         
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400,000us-gaap_PaymentsToAcquireLoansReceivable / dei_LegalEntityAxis = amrk_CollateralFinanceCorporationMember
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        | Stack Bowers Galleries | 
         
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        | Accounts, Notes, Loans and Financing Receivable [Line Items] | 
         
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        | Short term loan receivable | 
        
0us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = amrk_StackBowersGalleriesMember
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2,600,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = amrk_StackBowersGalleriesMember
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2,600,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = amrk_StackBowersGalleriesMember
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        | Rate of interest (percentage) | 
         
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5.50%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = amrk_StackBowersGalleriesMember
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        | Collateral Finance Corporation | 
         
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        | Accounts, Notes, Loans and Financing Receivable [Line Items] | 
         
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        | Short term loan receivable | 
         
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5,800,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = amrk_CollateralFinanceCorporationMember
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        | Premium on receivable | 
        
200,000us-gaap_ReceivableWithImputedInterestPremium / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = amrk_CollateralFinanceCorporationMember
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300,000us-gaap_ReceivableWithImputedInterestPremium / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = amrk_CollateralFinanceCorporationMember
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        | Rights Assumed for Portfolio on July 1, 2014 | Collateral Finance Corporation | 
         
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        | Accounts, Notes, Loans and Financing Receivable [Line Items] | 
         
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        | Short term loan receivable | 
        
2,000,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / dei_LegalEntityAxis = amrk_CollateralFinanceCorporationMember / us-gaap_RelatedPartyTransactionAxis = amrk_RightsAssumedforPortfolioonJulyFirstTwentyFourteenMember
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        | Collateral Finance Corporation | Rights Assumed for Portfolio on June 5, 2014 | 
         
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        | Accounts, Notes, Loans and Financing Receivable [Line Items] | 
         
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        | Short term loan receivable | 
        
1,300,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_AccountsNotesLoansAndFinancingReceivablesByLegalEntityOfCounterpartyTypeAxis = amrk_CollateralFinanceCorporationMember / us-gaap_RelatedPartyTransactionAxis = amrk_RightsAssumedforPortfolioonJuneFifthTwentyFourteenMember
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3,800,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_AccountsNotesLoansAndFinancingReceivablesByLegalEntityOfCounterpartyTypeAxis = amrk_CollateralFinanceCorporationMember / us-gaap_RelatedPartyTransactionAxis = amrk_RightsAssumedforPortfolioonJuneFifthTwentyFourteenMember
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        | Line of Credit [Member] | Stack Bowers Galleries | 
         
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        | Accounts, Notes, Loans and Financing Receivable [Line Items] | 
         
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        | Short term loan receivable | 
        
5,300,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_LongtermDebtTypeAxis = us-gaap_LineOfCreditMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = amrk_StackBowersGalleriesMember
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        | Line of credit, maximum borrowing capacity | 
         
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16,000,000.0us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity / us-gaap_LongtermDebtTypeAxis = us-gaap_LineOfCreditMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = amrk_StackBowersGalleriesMember
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        | Subsequent Event [Member] | 
         
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        | Accounts, Notes, Loans and Financing Receivable [Line Items] | 
         
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        | Short term loan receivable | 
         
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$ 3,100,000us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
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