Document and Entity Information - shares
9 Months Ended
Jun. 30, 2018
Jul. 30, 2018
Document And Entity Information [Abstract]    
Entity Registrant Name EMCORE CORP  
Entity Central Index Key 0000808326  
Document Type 10-Q  
Document Period End Date Jun. 30, 2018  
Document Fiscal Period Focus Q3  
Document Fiscal Year Focus 2018  
Current Fiscal Year End Date --09-30  
Entity Filer Category Accelerated Filer  
Amendment Flag false  
Entity Common Stock, Shares Outstanding   27,493,846