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Commitments and Contingencies (Other Disclosures) (Details) (USD $)
1 Months Ended 3 Months Ended 6 Months Ended 0 Months Ended
Mar. 31, 2012
Mar. 31, 2015
Dec. 31, 2014
Mar. 31, 2014
Mar. 31, 2015
Mar. 31, 2014
Sep. 23, 2014
Oct. 01, 2014
Loss Contingencies [Line Items]                
Operating leases, rent expense, net   $ 300,000us-gaap_OperatingLeasesRentExpenseNet   $ 400,000us-gaap_OperatingLeasesRentExpenseNet $ 700,000us-gaap_OperatingLeasesRentExpenseNet $ 800,000us-gaap_OperatingLeasesRentExpenseNet    
Fair value assumptions, credit adjusted risk-free rate, range minimal amount   3.25%emkr_FairValueAssumptionsCreditAdjustedRiskFreeRateRangeMinimalAmount     3.25%emkr_FairValueAssumptionsCreditAdjustedRiskFreeRateRangeMinimalAmount      
Fair value assumptions, credit adjusted risk-free rate, range maximum amount   5.78%emkr_FairValueAssumptionsCreditAdjustedRiskFreeRateRangeMaximumAmount     5.78%emkr_FairValueAssumptionsCreditAdjustedRiskFreeRateRangeMaximumAmount      
Asset retirement obligations reclassified to liabilities of discontinued operations   52,000us-gaap_AssetRetirementObligationAccretionExpense   41,000us-gaap_AssetRetirementObligationAccretionExpense 67,000us-gaap_AssetRetirementObligationAccretionExpense 85,000us-gaap_AssetRetirementObligationAccretionExpense    
Gain from change in estimate on ARO obligation     2,900,000us-gaap_AssetRetirementObligationRevisionOfEstimate   2,879,000us-gaap_AssetRetirementObligationRevisionOfEstimate      
Asset retirement obligation, revision in estimated cash flows   0emkr_AssetRetirementObligationGainLossfromRevisionofEstimates 800,000emkr_AssetRetirementObligationGainLossfromRevisionofEstimates 0emkr_AssetRetirementObligationGainLossfromRevisionofEstimates 845,000emkr_AssetRetirementObligationGainLossfromRevisionofEstimates 0emkr_AssetRetirementObligationGainLossfromRevisionofEstimates    
Business combination, indemnification assets, range of outcomes, value (up to $3.4 million) 3,400,000us-gaap_BusinessCombinationIndemnificationAssetsRangeOfOutcomesValueHigh              
Business combination, indemnification duration, period taken into account for 2 years              
Leasehold Improvements                
Loss Contingencies [Line Items]                
Decrease in property, plant, and equipment     (2,100,000)us-gaap_PropertyPlantAndEquipmentTransfersAndChanges
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LeaseholdImprovementsMember
         
Sumitomo Electric Industries, LTD                
Loss Contingencies [Line Items]                
Loss contingency, damages sought             $ 40,000,000us-gaap_LossContingencyDamagesSoughtValue
/ us-gaap_LitigationCaseAxis
= emkr_SumitomoElectricIndustriesLtdMember
 
Buildings | Property Subject to Operating Lease                
Loss Contingencies [Line Items]                
Number of leased buildings   6us-gaap_PropertySubjectToOrAvailableForOperatingLeaseNumberOfUnits
/ us-gaap_MajorPropertyClassAxis
= us-gaap_BuildingMember
/ us-gaap_PropertySubjectToOrAvailableForOperatingLeaseAxis
= us-gaap_PropertySubjectToOperatingLeaseMember
    6us-gaap_PropertySubjectToOrAvailableForOperatingLeaseNumberOfUnits
/ us-gaap_MajorPropertyClassAxis
= us-gaap_BuildingMember
/ us-gaap_PropertySubjectToOrAvailableForOperatingLeaseAxis
= us-gaap_PropertySubjectToOperatingLeaseMember
     
Lease term               3 years
Operating lease, term extension, option to extend               3 years