Document and Entity Information - USD ($)
$ in Billions
12 Months Ended
Apr. 30, 2017
Jun. 09, 2017
Oct. 30, 2016
Document and Entity Information [Abstract]      
Entity Registrant Name FINISAR CORP    
Entity Central Index Key 0001094739    
Current Fiscal Year End Date --04-30    
Entity Filer Category Large Accelerated Filer    
Document Type 10-K    
Document Period End Date Apr. 30, 2017    
Document Fiscal Year Focus 2017    
Document Fiscal Period Focus FY    
Amendment Flag false    
Entity Common Stock, Shares Outstanding   111,526,276  
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Public Float     $ 2.3