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Geographical Information Narrative (Details) (USD $)
3 Months Ended 6 Months Ended
Mar. 31, 2015
Dec. 31, 2014
Mar. 31, 2014
Mar. 31, 2015
Mar. 31, 2014
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 34.00%emkr_LongLivedAssetsLocatedInUnitedStatesPercentage     34.00%emkr_LongLivedAssetsLocatedInUnitedStatesPercentage   47.00%emkr_LongLivedAssetsLocatedInUnitedStatesPercentage    
Revision in estimated cash flows   $ (2,900,000)us-gaap_AssetRetirementObligationRevisionOfEstimate   $ (2,879,000)us-gaap_AssetRetirementObligationRevisionOfEstimate        
Asset retirement obligation, revision in estimated cash flows 0emkr_AssetRetirementObligationGainLossfromRevisionofEstimates 800,000emkr_AssetRetirementObligationGainLossfromRevisionofEstimates 0emkr_AssetRetirementObligationGainLossfromRevisionofEstimates 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 54.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueSegmentMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
  38.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueSegmentMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
62.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= us-gaap_SalesRevenueSegmentMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_CustomerConcentrationRiskMember
40.00%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             150,000,000us-gaap_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               $ 17,500,000us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration
/ us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis
= emkr_DigitalProductsBusinessMember