Document And Entity Information - shares	6 Months Ended
	Mar. 28, 2020	Apr. 15, 2020
Document Information [Line Items]
Entity Registrant Name	INSTEEL INDUSTRIES INC
Entity Central Index Key	0000764401
Trading Symbol	iiin
Current Fiscal Year End Date	--10-03
Entity Filer Category	Accelerated Filer
Entity Current Reporting Status	Yes
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Interactive Data Current	Yes
Entity Common Stock, Shares Outstanding (in shares)		19,260,725
Entity Shell Company	false
Document Type	10-Q
Document Period End Date	Mar. 28, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Amendment Flag	false
Title of 12(b) Security	Common Stock (No Par Value)