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Equity Narrative (Details) (USD $)
 0 Months Ended 3 Months Ended
Dec. 10, 2014
Dec. 31, 2014
Dec. 31, 2013
Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of equity incentive compensation plans maintained by the company   3emkr_NumberOfEquityIncentiveCompensationPlans    
Unvested restricted stock units   522,179us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber    
Share-based compensation, included in discontinued operations   $ 800,000emkr_DisposalGroupIncludingDiscontinuedOperationAllocatedSharebasedCompensation $ 300,000emkr_DisposalGroupIncludingDiscontinuedOperationAllocatedSharebasedCompensation  
Employee stock options        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock options, average minimum vesting period (in years)   4 years    
Stock options, average maximum vesting period (in years)   5 years    
Stock options, contractual life (in years)   10 years    
Unrecognized compensation expense   200,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember		    
Unrecognized compensation expense, period for recognition   2 years 6 months    
Restricted Stock Awards        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Award vesting period   3 years    
Restricted Stock Units        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Remaining unamortized stock-based compensation expense   1,100,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		    
Remaining unamortized stock-based compensation expense, period for recognition (in years)   1 year 0 months 0 days    
Unvested restricted stock units   522,179us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		   966,579us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
Outstanding non-vested RSUs aggregate intrinsic value   2,800,000emkr_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedAggregateIntrinsicValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		    
Outstanding non-vested RSUs weighted average remaining contractual term (in years)   0 years 6 months    
Share-based compensation arrangement by share-based payment award, equity instruments other than options, aggregate intrinsic value, vested   2,100,000us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueVested
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		 700,000us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueVested
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		  
Share-based compensation arrangement, by share-based payment award, options, vested and expected to vest, exercisable, number   500,000emkr_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndExpectedToVestExercisableNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		    
Share based compensation arrangement, by share based payment award, equity instruments other than options, expected to vest, intrinsic value   2,600,000emkr_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExpectedToVestIntrinsicValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		    
Share based compensation arrangement, by share based payment award, equity investments other than options, expected to vest, weighted average contractual term (in years)   0 years 6 months    
Weighted average grant date fair value, shares granted (USD per share)     $ 4.95us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		  
Vested (in shares) (300,000)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		 (406,450)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		    
Employee stock purchase plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Employee Stock Purchase Plan (ESPP), biannual plan duration   6 months    
Employee Stock Purchase Plan (ESPP), employee purchase price percentage   85.00%emkr_EmployeeStockPurchasePlanEsppEmployeePurchasePricePercentage
/ us-gaap_PlanNameAxis
= emkr_EmployeeStockPurchasePlanMember		    
Employee Stock Purchase Plan (ESPP), annual employee contribution limit percentage   10.00%emkr_EmployeeStockPurchasePlanEsppAnnualEmployeeContributionLimitPercentage
/ us-gaap_PlanNameAxis
= emkr_EmployeeStockPurchasePlanMember		    
Accelerated compensation cost   $ 25,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAcceleratedCompensationCost
/ us-gaap_PlanNameAxis
= emkr_EmployeeStockPurchasePlanMember