v3.19.1
Document And Entity Information - shares
6 Months Ended
Mar. 31, 2019
Apr. 30, 2019
Document and Entity Information [Abstract]    
Entity Registrant Name GRIFFON CORPORATION  
Document Type 10-Q  
Current Fiscal Year End Date --09-30  
Entity Common Stock, Shares Outstanding   46,800,571
Amendment Flag false  
Entity Central Index Key 0000050725  
Entity Filer Category Large Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Document Period End Date Mar. 31, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus (Q1,Q2,Q3,FY) Q2