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Geographical Information Narrative (Details) (USD $)
3 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Sep. 30, 2014
Dec. 10, 2014
Oct. 22, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
Percentage of long-lived assets located in the United States 28.00%emkr_LongLivedAssetsLocatedInUnitedStatesPercentage   47.00%emkr_LongLivedAssetsLocatedInUnitedStatesPercentage    
Revision in estimated cash flows $ (2,879,000)us-gaap_AssetRetirementObligationRevisionOfEstimate        
Asset retirement obligation, revision in estimated cash flows 845,000emkr_AssetRetirementObligationGainLossfromRevisionofEstimates 0emkr_AssetRetirementObligationGainLossfromRevisionofEstimates      
Leasehold Improvements          
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
Decrease in property, plant, and equipment (2,100,000)us-gaap_PropertyPlantAndEquipmentTransfersAndChanges
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LeaseholdImprovementsMember
       
Customer Concentration Risk | Sales Revenue, Segment          
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
Revenue by customer, percentage 50.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueSegmentMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
44.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueSegmentMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
     
Photovoltaics Business | Photovoltaics          
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
Asset purchase agreement, selling price       150,000,000emkr_DisposalGroupIncludingDiscontinuedOperationConsideration
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= emkr_PhotovoltaicsBusinessMember
/ us-gaap_StatementBusinessSegmentsAxis
= emkr_PhotovoltaicsMember
 
Digital Products Business          
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]          
Asset purchase agreement, selling price         $ 17,500,000emkr_DisposalGroupIncludingDiscontinuedOperationConsideration
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= emkr_DigitalProductsBusinessMember