Document And Entity Information - shares	9 Months Ended
	Jul. 01, 2017	Jul. 19, 2017
Document Information [Line Items]
Entity Registrant Name	INSTEEL INDUSTRIES INC
Entity Central Index Key	0000764401
Trading Symbol	iiin
Current Fiscal Year End Date	--09-30
Entity Filer Category	Accelerated Filer
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	No
Entity Common Stock, Shares Outstanding (in shares)		19,025,262
Document Type	10-Q
Document Period End Date	Jul. 01, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q3
Amendment Flag	false