Document And Entity Information - shares	3 Months Ended
	Dec. 30, 2017	Jan. 17, 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)		19,041,046
Document Type	10-Q
Document Period End Date	Dec. 30, 2017
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q1
Amendment Flag	false