Document And Entity Information
3 Months Ended
Dec. 31, 2018
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 46,763,601
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 Dec. 31, 2018
Document Fiscal Year Focus 2019
Document Fiscal Period Focus (Q1,Q2,Q3,FY) Q1