Document and Entity Information - USD ($)
$ in Millions
12 Months Ended
Sep. 30, 2017
Nov. 30, 2017
Mar. 31, 2017
Document And Entity Information [Abstract]      
Entity Registrant Name EMCORE CORPORATION    
Entity Central Index Key 0000808326    
Document Type 10-K    
Document Period End Date Sep. 30, 2017    
Document Fiscal Period Focus FY    
Document Fiscal Year Focus 2017    
Current Fiscal Year End Date --09-30    
Entity Filer Category Accelerated Filer    
Amendment Flag false    
Entity Common Stock, Shares Outstanding   27,128,382  
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Public Float     $ 239.0