Document And Entity Information - shares	9 Months Ended
	Jun. 30, 2018	Jul. 18, 2018
Document Information [Line Items]
Entity Registrant Name	INSTEEL INDUSTRIES INC
Entity Central Index Key	0000764401
Trading Symbol	iiin
Current Fiscal Year End Date	--09-29
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)		19,085,438
Document Type	10-Q
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Amendment Flag	false