Cover Page	3 Months Ended
	Dec. 31, 2019 shares
Cover page.
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Dec. 31, 2019
Document Transition Report	false
Entity File Number	1-06620
Entity Registrant Name	GRIFFON CORPORATION
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	11-1893410
Entity Address, Address Line One	712 Fifth Ave, 18th Floor
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10019
City Area Code	212
Local Phone Number	957-5000
Title of 12(b) Security	Common Stock, $0.25 par value
Trading Symbol	GFF
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	46,908,654
Current Fiscal Year End Date	--09-30
Amendment Flag	false
Entity Central Index Key	0000050725
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1