| 
           Goodwill and Intangible Assets (Intangible Assets) (Details) (USD $)
  
         | 
        6 Months Ended | 
         | 
      
      
        | 
           Dec. 31, 2014 
         | 
        
           Dec. 31, 2013 
         | 
        
           Jun. 30, 2014 
         | 
      
      
        | Indefinite-lived Intangible Assets [Line Items] | 
         
 | 
         
 | 
         
 | 
      
      
        | Gross carrying amount - finite lived intangible | 
        
$ 8,396,000amrk_IntangibleAssetsGrossCarryingAmount
 | 
         
 | 
        
$ 8,396,000amrk_IntangibleAssetsGrossCarryingAmount
 | 
      
      
        | Accumulated amortization | 
        
(5,835,000)us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
 | 
         
 | 
        
(5,643,000)us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
 | 
      
      
        | Net book value - finite lived intangible | 
        
2,561,000us-gaap_IntangibleAssetsNetExcludingGoodwill
 | 
         
 | 
        
2,753,000us-gaap_IntangibleAssetsNetExcludingGoodwill
 | 
      
      
        | Amortization expense related to intangible assets | 
        
200,000us-gaap_AmortizationOfIntangibleAssets
 | 
        
200,000us-gaap_AmortizationOfIntangibleAssets
 | 
         
 | 
      
      
        | Existing customer relationships | 
         
 | 
         
 | 
         
 | 
      
      
        | Indefinite-lived Intangible Assets [Line Items] | 
         
 | 
         
 | 
         
 | 
      
      
        | Gross carrying amount - finite lived intangible | 
        
5,747,000amrk_IntangibleAssetsGrossCarryingAmount / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerListsMember
 | 
         
 | 
        
5,747,000amrk_IntangibleAssetsGrossCarryingAmount / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerListsMember
 | 
      
      
        | Accumulated amortization | 
        
(3,640,000)us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerListsMember
 | 
         
 | 
        
(3,448,000)us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerListsMember
 | 
      
      
        | Net book value - finite lived intangible | 
        
2,107,000us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerListsMember
 | 
         
 | 
        
2,299,000us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerListsMember
 | 
      
      
        | Non-compete and other | 
         
 | 
         
 | 
         
 | 
      
      
        | Indefinite-lived Intangible Assets [Line Items] | 
         
 | 
         
 | 
         
 | 
      
      
        | Estimated useful lives | 
        4 years
 | 
         
 | 
         
 | 
      
      
        | Gross carrying amount - finite lived intangible | 
        
2,000,000amrk_IntangibleAssetsGrossCarryingAmount / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = amrk_NoncompeteAgreementsAndOtherIntangibleAssetsMember
 | 
         
 | 
        
2,000,000amrk_IntangibleAssetsGrossCarryingAmount / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = amrk_NoncompeteAgreementsAndOtherIntangibleAssetsMember
 | 
      
      
        | Accumulated amortization | 
        
(2,000,000)us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = amrk_NoncompeteAgreementsAndOtherIntangibleAssetsMember
 | 
         
 | 
        
(2,000,000)us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = amrk_NoncompeteAgreementsAndOtherIntangibleAssetsMember
 | 
      
      
        | Net book value - finite lived intangible | 
        
0us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = amrk_NoncompeteAgreementsAndOtherIntangibleAssetsMember
 | 
         
 | 
        
0us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = amrk_NoncompeteAgreementsAndOtherIntangibleAssetsMember
 | 
      
      
        | Employment agreement | 
         
 | 
         
 | 
         
 | 
      
      
        | Indefinite-lived Intangible Assets [Line Items] | 
         
 | 
         
 | 
         
 | 
      
      
        | Estimated useful lives | 
        3 years
 | 
         
 | 
         
 | 
      
      
        | Gross carrying amount - finite lived intangible | 
        
195,000amrk_IntangibleAssetsGrossCarryingAmount / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_EmploymentContractsMember
 | 
         
 | 
        
195,000amrk_IntangibleAssetsGrossCarryingAmount / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_EmploymentContractsMember
 | 
      
      
        | Accumulated amortization | 
        
(195,000)us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_EmploymentContractsMember
 | 
         
 | 
        
(195,000)us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_EmploymentContractsMember
 | 
      
      
        | Net book value - finite lived intangible | 
        
0us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_EmploymentContractsMember
 | 
         
 | 
        
0us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_EmploymentContractsMember
 | 
      
      
        | Purchased intangibles subject to amortization | 
         
 | 
         
 | 
         
 | 
      
      
        | Indefinite-lived Intangible Assets [Line Items] | 
         
 | 
         
 | 
         
 | 
      
      
        | Gross carrying amount - finite lived intangible | 
        
7,942,000amrk_IntangibleAssetsGrossCarryingAmount / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OtherIntangibleAssetsMember
 | 
         
 | 
        
7,942,000amrk_IntangibleAssetsGrossCarryingAmount / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OtherIntangibleAssetsMember
 | 
      
      
        | Accumulated amortization | 
        
(5,835,000)us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OtherIntangibleAssetsMember
 | 
         
 | 
        
(5,643,000)us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OtherIntangibleAssetsMember
 | 
      
      
        | Net book value - finite lived intangible | 
        
2,107,000us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OtherIntangibleAssetsMember
 | 
         
 | 
        
2,299,000us-gaap_IntangibleAssetsNetExcludingGoodwill / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OtherIntangibleAssetsMember
 | 
      
      
        | Trade-name | 
         
 | 
         
 | 
         
 | 
      
      
        | Indefinite-lived Intangible Assets [Line Items] | 
         
 | 
         
 | 
         
 | 
      
      
        | Gross carrying amount | 
        
454,000us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TrademarksMember
 | 
         
 | 
        
454,000us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TrademarksMember
 | 
      
      
        | Accumulated amortization | 
        
0us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TrademarksMember
 | 
         
 | 
        
0us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TrademarksMember
 | 
      
      
        | Net book value | 
        
$ 454,000amrk_IndefiniteLivedIntangibleAssetsNet / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TrademarksMember
 | 
         
 | 
        
$ 454,000amrk_IndefiniteLivedIntangibleAssetsNet / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TrademarksMember
 | 
      
      
        | Minimum | 
         
 | 
         
 | 
         
 | 
      
      
        | Indefinite-lived Intangible Assets [Line Items] | 
         
 | 
         
 | 
         
 | 
      
      
        | Estimated useful lives | 
        4 years
 | 
         
 | 
         
 | 
      
      
        | Minimum | Existing customer relationships | 
         
 | 
         
 | 
         
 | 
      
      
        | Indefinite-lived Intangible Assets [Line Items] | 
         
 | 
         
 | 
         
 | 
      
      
        | Estimated useful lives | 
        5 years
 | 
         
 | 
         
 | 
      
      
        | Maximum | 
         
 | 
         
 | 
         
 | 
      
      
        | Indefinite-lived Intangible Assets [Line Items] | 
         
 | 
         
 | 
         
 | 
      
      
        | Estimated useful lives | 
        15 years
 | 
         
 | 
         
 | 
      
      
        | Maximum | Existing customer relationships | 
         
 | 
         
 | 
         
 | 
      
      
        | Indefinite-lived Intangible Assets [Line Items] | 
         
 | 
         
 | 
         
 | 
      
      
        | Estimated useful lives | 
        15 years
 | 
         
 | 
         
 |