Quarterly report pursuant to Section 13 or 15(d)

Receivables (Components of Receivables and Secured Loans - Trading) (Details)

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Receivables (Components of Receivables and Secured Loans - Trading) (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Jun. 30, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Receivables and secured loans gross $ 107,924amrk_ReceivablesAndSecuredLoansGrossTradingOperations $ 80,670amrk_ReceivablesAndSecuredLoansGrossTradingOperations
Subtotal 65,360amrk_ReceivablesExcludingSecuredLoansDerivativeAssetsGrossTradingOps 39,409amrk_ReceivablesExcludingSecuredLoansDerivativeAssetsGrossTradingOps
Secured loans 41,764us-gaap_NotesAndLoansReceivableNetCurrent 41,261us-gaap_NotesAndLoansReceivableNetCurrent
Secured loans (long-term portion) 800us-gaap_NotesAndLoansReceivableNetNoncurrent 0us-gaap_NotesAndLoansReceivableNetNoncurrent
Less: allowance for doubtful accounts (30)us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent (30)us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent
Subtotal 107,894amrk_ReceivablesAndSecuredLoansFairValueDisclosure 80,640amrk_ReceivablesAndSecuredLoansFairValueDisclosure
Derivative assets — open sale and purchase commitments, net 2,428amrk_DerivativeAssetsOpenPurchaseAndSalesCommitments 22,170amrk_DerivativeAssetsOpenPurchaseAndSalesCommitments
Derivative assets — futures contracts 6,174amrk_DerivativeAssetsFuturesContractsCurrent 0amrk_DerivativeAssetsFuturesContractsCurrent
Derivative assets — forward contracts 9,510amrk_DerivativeAssetsForwardContracts 14amrk_DerivativeAssetsForwardContracts
Receivables, net 126,006amrk_ReceivablesAndSecuredLoansNetTradingOperations 102,824amrk_ReceivablesAndSecuredLoansNetTradingOperations
Customer trade receivables    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Receivables and secured loans gross 32,129amrk_ReceivablesAndSecuredLoansGrossTradingOperations
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_TradeAccountsReceivableMember
1,744amrk_ReceivablesAndSecuredLoansGrossTradingOperations
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= us-gaap_TradeAccountsReceivableMember
Wholesale trade advances    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Receivables and secured loans gross 11,583amrk_ReceivablesAndSecuredLoansGrossTradingOperations
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= amrk_WholesaleTradeAdvancesMember
4,586amrk_ReceivablesAndSecuredLoansGrossTradingOperations
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= amrk_WholesaleTradeAdvancesMember
Due from brokers    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Receivables and secured loans gross $ 21,648amrk_ReceivablesAndSecuredLoansGrossTradingOperations
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= amrk_DueFromBrokersMember
$ 33,079amrk_ReceivablesAndSecuredLoansGrossTradingOperations
/ us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis
= amrk_DueFromBrokersMember