v3.8.0.1
Document And Entity Information - USD ($)
12 Months Ended
Sep. 30, 2017
Oct. 31, 2017
Mar. 31, 2017
Document and Entity Information [Abstract]      
Entity Registrant Name GRIFFON CORP    
Document Type 10-K    
Current Fiscal Year End Date --09-30    
Entity Common Stock, Shares Outstanding   47,219,519  
Entity Public Float     $ 882,000,000
Amendment Flag false    
Entity Central Index Key 0000050725    
Entity Current Reporting Status Yes    
Entity Voluntary Filers No    
Entity Filer Category Large Accelerated Filer    
Entity Well-known Seasoned Issuer No    
Document Period End Date Sep. 30, 2017    
Document Fiscal Year Focus 2017    
Document Fiscal Period Focus FY