Quarterly report pursuant to Section 13 or 15(d)

Hedging Transactions (Narrative) (Details)

v2.4.1.9
Hedging Transactions (Narrative) (Details) (USD $)
3 Months Ended 9 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Mar. 31, 2015
Mar. 31, 2014
Jun. 30, 2014
Derivative [Line Items]          
Realized gain (loss) on future commodity contracts, net $ (10,309,000)us-gaap_DerivativeGainLossOnDerivativeNet $ (21,122,000)us-gaap_DerivativeGainLossOnDerivativeNet $ (44,831,000)us-gaap_DerivativeGainLossOnDerivativeNet $ (31,144,000)us-gaap_DerivativeGainLossOnDerivativeNet  
Derivative usual settlement period     2 days    
Derivative open positions expected settlement period     30 days    
Unrealized losses on foreign exchange (123,000)us-gaap_ForeignCurrencyTransactionGainLossUnrealized (60,000)us-gaap_ForeignCurrencyTransactionGainLossUnrealized (207,000)us-gaap_ForeignCurrencyTransactionGainLossUnrealized 0us-gaap_ForeignCurrencyTransactionGainLossUnrealized  
Foreign Exchange          
Derivative [Line Items]          
Open inventory sale commitments 300,000amrk_OpenInventorySaleandPurchaseCommitmentsnet
/ amrk_CommitmentTypeAxis
= us-gaap_ForeignExchangeMember
  300,000amrk_OpenInventorySaleandPurchaseCommitmentsnet
/ amrk_CommitmentTypeAxis
= us-gaap_ForeignExchangeMember
  2,700,000amrk_OpenInventorySaleandPurchaseCommitmentsnet
/ amrk_CommitmentTypeAxis
= us-gaap_ForeignExchangeMember
Forward contracts          
Derivative [Line Items]          
Open inventory sale commitments $ 2,200,000amrk_OpenInventorySaleandPurchaseCommitmentsnet
/ amrk_CommitmentTypeAxis
= us-gaap_ForwardContractsMember
  $ 2,200,000amrk_OpenInventorySaleandPurchaseCommitmentsnet
/ amrk_CommitmentTypeAxis
= us-gaap_ForwardContractsMember
  $ 3,800,000amrk_OpenInventorySaleandPurchaseCommitmentsnet
/ amrk_CommitmentTypeAxis
= us-gaap_ForwardContractsMember