Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies (Customer Concentrations) (Details)

v2.4.1.9
Summary of Significant Accounting Policies (Customer Concentrations) (Details) (USD $)
3 Months Ended 9 Months Ended 12 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Mar. 31, 2015
Mar. 31, 2014
Jun. 30, 2014
Concentration Risk [Line Items]          
Total revenue $ 1,624,495,000us-gaap_SalesRevenueGoodsNet $ 1,581,590,000us-gaap_SalesRevenueGoodsNet $ 4,616,832,000us-gaap_SalesRevenueGoodsNet $ 4,566,306,000us-gaap_SalesRevenueGoodsNet  
Total accounts receivable, net (excluding secured loans and derivative assets) 55,862,000amrk_ReceivablesExcludingSecuredLoansDerivativeAssetsGrossTradingOps   55,862,000amrk_ReceivablesExcludingSecuredLoansDerivativeAssetsGrossTradingOps   39,409,000amrk_ReceivablesExcludingSecuredLoansDerivativeAssetsGrossTradingOps
Derivative asset 6,390,000us-gaap_DerivativeAssets   6,390,000us-gaap_DerivativeAssets   22,184,000us-gaap_DerivativeAssets
Revenue | Customer concentrations          
Concentration Risk [Line Items]          
Total revenue 1,624,495,000us-gaap_SalesRevenueGoodsNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
1,581,590,000us-gaap_SalesRevenueGoodsNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
4,616,832,000us-gaap_SalesRevenueGoodsNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
4,566,306,000us-gaap_SalesRevenueGoodsNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
 
Concentration risk, percentage 100.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
100.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
  100.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
 
Accounts receivable | Customer concentrations          
Concentration Risk [Line Items]          
Total accounts receivable, net (excluding secured loans and derivative assets) 55,862,000amrk_ReceivablesExcludingSecuredLoansDerivativeAssetsGrossTradingOps
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
  55,862,000amrk_ReceivablesExcludingSecuredLoansDerivativeAssetsGrossTradingOps
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
  39,409,000amrk_ReceivablesExcludingSecuredLoansDerivativeAssetsGrossTradingOps
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
Concentration risk, percentage     100.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
  100.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
Secured loans | Customer concentrations          
Concentration Risk [Line Items]          
Total secured loans 46,259,000us-gaap_NotesReceivableNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
  46,259,000us-gaap_NotesReceivableNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
  41,261,000us-gaap_NotesReceivableNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
Concentration risk, percentage     100.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
  100.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
HSBC Bank USA | Revenue | Customer concentrations          
Concentration Risk [Line Items]          
Total revenue 481,036,000us-gaap_SalesRevenueGoodsNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_HSBCBankUSAMember
454,899,000us-gaap_SalesRevenueGoodsNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_HSBCBankUSAMember
1,464,027,000us-gaap_SalesRevenueGoodsNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_HSBCBankUSAMember
1,160,592,000us-gaap_SalesRevenueGoodsNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_HSBCBankUSAMember
 
Concentration risk, percentage 29.60%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_HSBCBankUSAMember
28.80%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_HSBCBankUSAMember
31.70%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_HSBCBankUSAMember
25.40%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_HSBCBankUSAMember
 
Veris Gold | Accounts receivable | Customer concentrations          
Concentration Risk [Line Items]          
Total accounts receivable, net (excluding secured loans and derivative assets) 7,516,000amrk_ReceivablesExcludingSecuredLoansDerivativeAssetsGrossTradingOps
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_VerisGoldMember
  7,516,000amrk_ReceivablesExcludingSecuredLoansDerivativeAssetsGrossTradingOps
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_VerisGoldMember
  0amrk_ReceivablesExcludingSecuredLoansDerivativeAssetsGrossTradingOps
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_VerisGoldMember
Concentration risk, percentage     13.50%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_VerisGoldMember
0.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_VerisGoldMember
 
Ocean Partners | Accounts receivable | Customer concentrations          
Concentration Risk [Line Items]          
Total accounts receivable, net (excluding secured loans and derivative assets) 23,174,000amrk_ReceivablesExcludingSecuredLoansDerivativeAssetsGrossTradingOps
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_OceanPartnersMember
  23,174,000amrk_ReceivablesExcludingSecuredLoansDerivativeAssetsGrossTradingOps
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_OceanPartnersMember
  0amrk_ReceivablesExcludingSecuredLoansDerivativeAssetsGrossTradingOps
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_OceanPartnersMember
Concentration risk, percentage     41.50%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_OceanPartnersMember
0.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_OceanPartnersMember
 
Royal Canadian Mint | Accounts receivable | Customer concentrations          
Concentration Risk [Line Items]          
Total accounts receivable, net (excluding secured loans and derivative assets) 8,123,000amrk_ReceivablesExcludingSecuredLoansDerivativeAssetsGrossTradingOps
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_RoyalCanadianMintMember
  8,123,000amrk_ReceivablesExcludingSecuredLoansDerivativeAssetsGrossTradingOps
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_RoyalCanadianMintMember
  2,244,000amrk_ReceivablesExcludingSecuredLoansDerivativeAssetsGrossTradingOps
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_RoyalCanadianMintMember
Concentration risk, percentage     14.50%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_RoyalCanadianMintMember
5.70%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_RoyalCanadianMintMember
 
Customer A | Secured loans | Customer concentrations          
Concentration Risk [Line Items]          
Total secured loans 4,900,000us-gaap_NotesReceivableNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_CustomerMember
  4,900,000us-gaap_NotesReceivableNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_CustomerMember
  4,200,000us-gaap_NotesReceivableNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_CustomerMember
Concentration risk, percentage     10.60%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_CustomerMember
  10.30%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_CustomerMember
Customer B | Secured loans | Customer concentrations          
Concentration Risk [Line Items]          
Total secured loans 5,045,000us-gaap_NotesReceivableNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_CustomerBMember
  5,045,000us-gaap_NotesReceivableNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_CustomerBMember
  4,103,000us-gaap_NotesReceivableNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_CustomerBMember
Concentration risk, percentage     10.90%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_CustomerBMember
  9.90%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_CustomerBMember
Customer C | Secured loans | Customer concentrations          
Concentration Risk [Line Items]          
Total secured loans 5,000,000us-gaap_NotesReceivableNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_CustomercMember
  5,000,000us-gaap_NotesReceivableNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_CustomercMember
  0us-gaap_NotesReceivableNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_CustomercMember
Concentration risk, percentage     10.80%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_CustomercMember
  0.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_CustomercMember
Customer D | Secured loans | Customer concentrations          
Concentration Risk [Line Items]          
Total secured loans 5,622,000us-gaap_NotesReceivableNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_CustomerDMember
  5,622,000us-gaap_NotesReceivableNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_CustomerDMember
  3,771,000us-gaap_NotesReceivableNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_CustomerDMember
Concentration risk, percentage     12.20%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_CustomerDMember
  9.10%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_CustomerDMember
Major Customers | Revenue | Customer concentrations          
Concentration Risk [Line Items]          
Total revenue 481,036,000us-gaap_SalesRevenueGoodsNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_MajorCustomersMember
454,899,000us-gaap_SalesRevenueGoodsNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_MajorCustomersMember
1,464,027,000us-gaap_SalesRevenueGoodsNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_MajorCustomersMember
1,160,592,000us-gaap_SalesRevenueGoodsNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_MajorCustomersMember
 
Concentration risk, percentage 29.60%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_MajorCustomersMember
28.80%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_MajorCustomersMember
31.70%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_MajorCustomersMember
25.40%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueGoodsNetMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_MajorCustomersMember
 
Major Customers | Accounts receivable | Customer concentrations          
Concentration Risk [Line Items]          
Total accounts receivable, net (excluding secured loans and derivative assets) 38,813,000amrk_ReceivablesExcludingSecuredLoansDerivativeAssetsGrossTradingOps
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_MajorCustomersMember
  38,813,000amrk_ReceivablesExcludingSecuredLoansDerivativeAssetsGrossTradingOps
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_MajorCustomersMember
  2,244,000amrk_ReceivablesExcludingSecuredLoansDerivativeAssetsGrossTradingOps
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_MajorCustomersMember
Concentration risk, percentage     69.50%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_MajorCustomersMember
  5.70%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_AccountsReceivableMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_MajorCustomersMember
Major Customers | Secured loans | Customer concentrations          
Concentration Risk [Line Items]          
Total secured loans $ 20,567,000us-gaap_NotesReceivableNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_MajorCustomersMember
  $ 20,567,000us-gaap_NotesReceivableNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_MajorCustomersMember
  $ 12,074,000us-gaap_NotesReceivableNet
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_MajorCustomersMember
Concentration risk, percentage     44.50%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_MajorCustomersMember
  29.30%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_LoansAndFinanceReceivablesMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
/ us-gaap_MajorCustomersAxis
= amrk_MajorCustomersMember