Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity (Spin-off) (Details)

v2.4.1.9
Stockholders' Equity (Spin-off) (Details) (USD $)
In Millions, except Share data, unless otherwise specified
0 Months Ended 9 Months Ended 0 Months Ended
Mar. 19, 2014
Mar. 31, 2015
Mar. 14, 2014
Mar. 19, 2014
Mar. 17, 2014
Class of Stock [Line Items]          
Exchange ratio based on average closing price for SGI shares 0.2397amrk_EquityAwardExchangeRatioofFormerParentsAwardstoReplacementAwardsofParent        
Common stock exchange ratio   4.1717amrk_InverseEquityAwardExchangeRatioDenominator      
SGI (Former Parent)          
Class of Stock [Line Items]          
Three day weighted average share price before spin-off ( per share)     $ 3.32amrk_FormerParentThreeDayAverageSharePricesBeforeSpinoff
/ dei_LegalEntityAxis
= amrk_FormerParentSGIMember
   
Share price 14.00us-gaap_SharePrice
/ dei_LegalEntityAxis
= amrk_FormerParentSGIMember
  $ 3.37us-gaap_SharePrice
/ dei_LegalEntityAxis
= amrk_FormerParentSGIMember
14.00us-gaap_SharePrice
/ dei_LegalEntityAxis
= amrk_FormerParentSGIMember
$ 13.30us-gaap_SharePrice
/ dei_LegalEntityAxis
= amrk_FormerParentSGIMember
SGI          
Class of Stock [Line Items]          
Three day weighted average share price after spin-off ( per share) 13.85amrk_ParentThreeDayAverageSharePriceAfterSpinoff
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
       
Awards assumed from SGI spin-off          
Class of Stock [Line Items]          
Grants during the period (shares) 249,846us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_PlanNameAxis
= amrk_AwardsAssumedfromSGIPlanrelatedtospinoffMember
       
Total compensation cost not yet recognized   0.4us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ us-gaap_PlanNameAxis
= amrk_AwardsAssumedfromSGIPlanrelatedtospinoffMember
     
Restricted Stock Units (RSUs)          
Class of Stock [Line Items]          
Period for recognition of nonvested awards   11 months 22 days      
Restricted Stock Units (RSUs) | Awards assumed from SGI spin-off          
Class of Stock [Line Items]          
Grants during the period (shares) 130,646us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_PlanNameAxis
= amrk_AwardsAssumedfromSGIPlanrelatedtospinoffMember
    130,646us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_PlanNameAxis
= amrk_AwardsAssumedfromSGIPlanrelatedtospinoffMember
 
Total compensation cost not yet recognized, other than options   0.1us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_PlanNameAxis
= amrk_AwardsAssumedfromSGIPlanrelatedtospinoffMember
     
Restricted Stock Units (RSUs) | Awards assumed from SGI spin-off | Issued to A-Mark Employees          
Class of Stock [Line Items]          
Grants during the period (shares) 50,340us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ dei_LegalEntityAxis
= amrk_IssuedtoAMarkEmployeesMember
/ us-gaap_PlanNameAxis
= amrk_AwardsAssumedfromSGIPlanrelatedtospinoffMember
       
Stock Appreciation Rights (SARs) | Awards assumed from SGI spin-off          
Class of Stock [Line Items]          
Grants during the period (shares) 8,990us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_StockAppreciationRightsSARSMember
/ us-gaap_PlanNameAxis
= amrk_AwardsAssumedfromSGIPlanrelatedtospinoffMember
    8,990us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_StockAppreciationRightsSARSMember
/ us-gaap_PlanNameAxis
= amrk_AwardsAssumedfromSGIPlanrelatedtospinoffMember
 
Total compensation cost not yet recognized, other than options   0us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions
/ us-gaap_AwardTypeAxis
= us-gaap_StockAppreciationRightsSARSMember
/ us-gaap_PlanNameAxis
= amrk_AwardsAssumedfromSGIPlanrelatedtospinoffMember
     
Stock Appreciation Rights (SARs) | Awards assumed from SGI spin-off | Issued to A-Mark Employees          
Class of Stock [Line Items]          
Grants during the period (shares) 8,990us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_StockAppreciationRightsSARSMember
/ dei_LegalEntityAxis
= amrk_IssuedtoAMarkEmployeesMember
/ us-gaap_PlanNameAxis
= amrk_AwardsAssumedfromSGIPlanrelatedtospinoffMember
       
Stock Options          
Class of Stock [Line Items]          
Period for recognition of nonvested awards   2 years 6 months 26 days      
Stock Options | Awards assumed from SGI spin-off | Issued to A-Mark Employees          
Class of Stock [Line Items]          
Grants during the period (shares) 216,943us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ dei_LegalEntityAxis
= amrk_IssuedtoAMarkEmployeesMember
/ us-gaap_PlanNameAxis
= amrk_AwardsAssumedfromSGIPlanrelatedtospinoffMember