Document And Entity Information - shares	9 Months Ended
	Jun. 30, 2018	Jul. 31, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	GRIFFON CORP
Document Type	10-Q
Current Fiscal Year End Date	--09-30
Entity Common Stock, Shares Outstanding		45,615,377
Amendment Flag	false
Entity Central Index Key	0000050725
Entity Filer Category	Large Accelerated Filer
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus (Q1,Q2,Q3,FY)	Q3