Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies (Derivative Instruments) (Details)

v2.4.1.9
Summary of Significant Accounting Policies (Derivative Instruments) (Details) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 6 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2014
Dec. 31, 2013
Derivative [Line Items]        
Realized loss on future commodity contracts, net $ (28,166)us-gaap_DerivativeGainLossOnDerivativeNet $ 7,567us-gaap_DerivativeGainLossOnDerivativeNet $ (34,522)us-gaap_DerivativeGainLossOnDerivativeNet $ (10,022)us-gaap_DerivativeGainLossOnDerivativeNet
Futures Commodity And Forwards Contracts And Open Purchase And Sale Commitments [Member]        
Derivative [Line Items]        
Unrealized gain (loss) on open future commodity and forward contracts and open sale and purchase commitments, net 9,006us-gaap_UnrealizedGainLossOnDerivatives
/ us-gaap_DerivativeInstrumentRiskAxis
= amrk_FuturesCommodityAndForwardsContractsAndOpenPurchaseAndSaleCommitmentsMember
14,047us-gaap_UnrealizedGainLossOnDerivatives
/ us-gaap_DerivativeInstrumentRiskAxis
= amrk_FuturesCommodityAndForwardsContractsAndOpenPurchaseAndSaleCommitmentsMember
10,284us-gaap_UnrealizedGainLossOnDerivatives
/ us-gaap_DerivativeInstrumentRiskAxis
= amrk_FuturesCommodityAndForwardsContractsAndOpenPurchaseAndSaleCommitmentsMember
(1,839)us-gaap_UnrealizedGainLossOnDerivatives
/ us-gaap_DerivativeInstrumentRiskAxis
= amrk_FuturesCommodityAndForwardsContractsAndOpenPurchaseAndSaleCommitmentsMember
Commodity Contract        
Derivative [Line Items]        
Realized loss on future commodity contracts, net $ (37,172)us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
$ (6,480)us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
$ (44,806)us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember
$ (8,183)us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CommodityContractMember