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Commitments and Contingencies Asset Retirement Obligation (Details) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 6 Months Ended 12 Months Ended
Mar. 31, 2015
Dec. 31, 2014
Mar. 31, 2014
Mar. 31, 2015
Mar. 31, 2014
Sep. 30, 2014
Asset Retirement Obligations            
Balance at September 30, 2014   $ 5,263us-gaap_AssetRetirementObligation   $ 5,263us-gaap_AssetRetirementObligation    
Asset retirement obligations reclassified to liabilities of discontinued operations           (720)emkr_AssetRetirementObligationAmountReclassifiedToDiscontinuedOperationsLiability
Asset retirement obligation, including discontinued operations           4,543emkr_AssetRetirementObligationafterReclassificationtoDiscontinuedOperations
Asset retirement obligations reclassified to liabilities of discontinued operations 52us-gaap_AssetRetirementObligationAccretionExpense   41us-gaap_AssetRetirementObligationAccretionExpense 67us-gaap_AssetRetirementObligationAccretionExpense 85us-gaap_AssetRetirementObligationAccretionExpense  
Revision in estimated cash flows   (2,900)us-gaap_AssetRetirementObligationRevisionOfEstimate   (2,879)us-gaap_AssetRetirementObligationRevisionOfEstimate    
Balance at end of period $ 1,731us-gaap_AssetRetirementObligation     $ 1,731us-gaap_AssetRetirementObligation   $ 5,263us-gaap_AssetRetirementObligation