Significant Accounting Policies (Policies)	12 Months Ended
Oct. 01, 2016
Accounting Policies [Abstract]
Fiscal Period, Policy [Policy Text Block]	Fiscal year. Our fiscal year is the 52 or 53 weeks ending on the Saturday closest to September 30. Fiscal years 2016 and 2014 were 52-week periods and fiscal year 2015 was a 53-week period. All references to years relate to fiscal years rather than calendar years.
Consolidation, Policy [Policy Text Block]	Principles of consolidation . The consolidated financial statements include the accounts of Insteel and our subsidiaries. All significant intercompany transactions and accounts have been eliminated in consolidation.
Use of Estimates, Policy [Policy Text Block]	Use of estimates. The preparation of financial statements in conformity with accounting principles generally accepted in the United States (“U.S.” and such accounting principles, “GAAP”) requires us to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. There is no assurance that actual results will not differ from these estimates.
Cash and Cash Equivalents, Policy [Policy Text Block]	Cash equivalents . We consider all highly liquid investments purchased with original maturities of three months or less to be cash equivalents.
Concentration Risk, Credit Risk, Policy [Policy Text Block]	Concentration of c redit r isk . Financial instruments that subject us to concentrations of credit risk consist principally of cash and cash equivalents and trade accounts receivable. Our cash is principally concentrated at one financial institution, which at times exceeds federally insured limits. We are exposed to credit risk in the event of default by institutions in which our cash and cash equivalents are held and by customers to the extent of the amounts recorded on the balance sheet. We invest excess cash primarily in money market funds, which are highly liquid securities. The majority of our accounts receivable are due from customers that are located in the U.S., and are generally not secured by collateral depending upon the creditworthiness of the account. We provide an allowance for doubtful accounts based upon our assessment of the credit risk of specific customers, historical trends and other information. We write off accounts receivable when they become uncollectible. There is no disproportionate concentration of credit risk.
Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block]	Stock-based compensation. We account for stock-based compensation in accordance with the fair value recognition provisions of Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 718, Compensation – Stock Compensation, which requires stock-based compensation expense to be recognized in net earnings based on the fair value of the award on the date of the grant. We determine the fair value of stock options issued by using a Monte Carlo valuation model at the grant date, which considers a range of assumptions including the expected term, volatility, dividend yield and risk-free interest rate.
Revenue Recognition, Policy [Policy Text Block]	Revenue recognition . We recognize revenue from product sales when products are shipped and risk of loss and title has passed to the customer. Sales taxes collected from customers are excluded from revenues and recorded on a net basis.
Shipping and Handling Cost, Policy [Policy Text Block]	Shipping and handling costs . We include all of the outbound freight, shipping and handling costs associated with the shipment of products to customers in cost of sales. Any amounts paid by customers to us for shipping and handling are recorded in net sales on the consolidated statements of operations.
Inventory, Policy [Policy Text Block]	Inventories . Inventories are valued at the lower of weighted average cost (which approximates computation on a first-in, first-out basis) or market (net realizable value or replacement cost). The valuation of inventory includes the costs for material, labor and manufacturing overhead.
Property, Plant and Equipment, Impairment [Policy Text Block]	Property, plant and equipment. Property, plant and equipment are recorded at cost or fair market value in the case of the assets acquired through acquisitions, or otherwise at reduced values to the extent there have been asset impairment write-downs. Expenditures for maintenance and repairs are charged directly to expense when incurred, while major improvements are capitalized. Depreciation is computed for financial reporting purposes principally by use of the straight-line method over the following estimated useful lives: machinery and equipment, 3 - 15 years; buildings, 10 - 30 years; and land improvements, 5 - 15 years. Depreciation expense was approximately $10.4 million in 2016, $10.9 million in 2015 and $9.8 million in 2014 and reflected in cost of sales and selling, general and administrative expense (“SG&A expense”) in the consolidated statements of operations. Capitalized software is amortized over the shorter of the estimated useful life or 5 years and reflected in SG&A expense in the consolidated statements of operations. No interest costs were capitalized in 2016, 2015 and 2014.
Goodwill and Intangible Assets, Goodwill, Policy [Policy Text Block]	Goodwill . Goodwill is the excess of cost over the fair value of net assets of businesses acquired. Goodwill is not amortized but is tested annually for impairment and whenever events or circumstances change that would make it more likely than not that an impairment may have occurred. We perform our annual impairment analysis as of the first day of the fourth quarter each year. The evaluation of impairment involves comparing the current estimated fair value of the reporting unit to its recorded value, including goodwill. We perform a qualitative assessment to determine whether it is more likely than not that the fair value of the reporting unit is less than its carrying amount. It may be necessary to perform a quantitative analysis where a discounted cash flow model is used to determine the current estimated fair value of the reporting unit. Key assumptions used to determine the fair value of the reporting unit as part of our annual testing (and any required interim testing) include: (a) expected cash flows for the five-year period following the testing date; (b) an estimated terminal value using a terminal year growth rate based on the growth prospects of the reporting unit; (c) a discount rate based on our estimated after-tax weighted average cost of capital; and (d) a probability-weighted scenario approach by which varying cash flows are assigned to alternative scenarios based on their likelihood of occurrence. In developing these assumptions, we consider historical and anticipated future results, general economic and market conditions, the impact of planned business and operational strategies and all available information at the time the fair value of the reporting unit is estimated. Assumptions in estimating future cash flows are subject to a high degree of judgment and complexity. Changes in assumptions and estimates may affect the fair value of goodwill and could result in impairment charges in future periods. Based on the results of our impairment analysis, no goodwill impairment losses were recognized in the consolidated statements of operations for 2016 . Subsequent to the analysis, there have been no events or circumstances that indicate any potential impairment of goodwill.
Other Assets [Policy Text Block]	Other assets. Other assets consist principally of capitalized financing costs and the cash surrender value of life insurance policies. Capitalized financing costs are amortized using the straight-line method, which approximates the effective interest method over the term of the related credit agreement, and reflected in interest expense in the consolidated statements of operations.
Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block]	Long-lived assets . Long-lived assets include property, plant and equipment and identifiable intangible assets with definite useful lives. Finite-lived intangible assets are amortized over their estimated useful lives. Our intangible assets consist of customer relationships, developed technology and know-how and non-competition agreements that are being amortized on a straight-line basis over their finite useful lives (see Note 7 to the consolidated financial statements). We assess the impairment of long-lived assets whenever events or changes in circumstances indicate that the carrying value may not be fully recoverable. When we determine that the carrying value of such assets may not be recoverable, we measure recoverability based on the undiscounted cash flows expected to be generated by the related asset or asset group. If it is determined that an impairment loss has occurred, the loss is recognized in the period in which it is incurred and is calculated as the difference between the carrying value and the present value of estimated future net cash flows or comparable market values. During 2016 and 2015, we recorded $20,000 and $0.3 million, respectively, of impairment charges related to long-lived assets resulting from the consolidation of our PC strand operations with the closure of the Newnan, Georgia facility (see Note 5 to the consolidated financial statements). There were no impairment losses in 2014
Fair Value Measurement, Policy [Policy Text Block]	Fair value of financial instruments . The carrying amounts for cash and cash equivalents, accounts receivable, and accounts payable and accrued expenses approximate fair value because of their short maturities.
Income Tax, Policy [Policy Text Block]	Income taxes. Income taxes are based on pretax financial accounting income. Deferred tax assets and liabilities are recognized for the expected tax consequences of temporary differences between the tax bases of assets and liabilities and their reported amounts. We assess the need to establish a valuation allowance against deferred tax assets to the extent we no longer believe it is more likely than not that the tax assets will be fully realized.
Earnings Per Share, Policy [Policy Text Block]	Earnings per share. Basic earnings per share (“EPS”) are computed by dividing earnings available to common shareholders by the weighted average number of shares of common stock outstanding during the period. Diluted EPS are computed by dividing earnings available to common shareholders by the weighted average number of shares of common stock and other dilutive equity securities outstanding during the period. Securities that have the effect of increasing EPS are considered to be antidilutive and are not included in the computation of diluted EPS.

Significant Accounting Policies (Policies)

12 Months Ended

Oct. 01, 2016

Fiscal Period, Policy [Policy Text Block]

Fiscal year.

Our fiscal year is the 52 or 53 weeks ending on the Saturday closest to September 30. Fiscal years 2016 and 2014 were 52-week periods and fiscal year 2015 was a 53-week period. All references to years relate to fiscal years rather than calendar years.

Consolidation, Policy [Policy Text Block]

Principles of consolidation

The consolidated financial statements include the accounts of Insteel and our subsidiaries. All significant intercompany transactions and accounts have been eliminated in consolidation.

Use of Estimates, Policy [Policy Text Block]

Use of estimates.

The preparation of financial statements in conformity with accounting principles generally accepted in the United States (“U.S.” and such accounting principles, “GAAP”) requires us to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. There is no assurance that actual results will not differ from these estimates.

Cash and Cash Equivalents, Policy [Policy Text Block]

Cash equivalents

We consider all highly liquid investments purchased with original maturities of three months or less to be cash equivalents.

Concentration Risk, Credit Risk, Policy [Policy Text Block]

Concentration of

redit

isk

Financial instruments that subject us to concentrations of credit risk consist principally of cash and cash equivalents and trade accounts receivable. Our cash is principally concentrated at one financial institution, which at times exceeds federally insured limits. We are exposed to credit risk in the event of default by institutions in which our cash and cash equivalents are held and by customers to the extent of the amounts recorded on the balance sheet. We invest excess cash primarily in money market funds, which are highly liquid securities.

The majority of our accounts receivable are due from customers that are located in the U.S., and are generally not secured by collateral depending upon the creditworthiness of the account. We provide an allowance for doubtful accounts based upon our assessment of the credit risk of specific customers, historical trends and other information. We write off accounts receivable when they become uncollectible. There is no disproportionate concentration of credit risk.

Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block]

Stock-based compensation.

We account for stock-based compensation in accordance with the fair value recognition provisions of Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 718, Compensation – Stock Compensation, which requires stock-based compensation expense to be recognized in net earnings based on the fair value of the award on the date of the grant. We determine the fair value of stock options issued by using a Monte Carlo valuation model at the grant date, which considers a range of assumptions including the expected term, volatility, dividend yield and risk-free interest rate.

Revenue Recognition, Policy [Policy Text Block]

Revenue recognition

We recognize revenue from product sales when products are shipped and risk of loss and title has passed to the customer. Sales taxes collected from customers are excluded from revenues and recorded on a net basis.

Shipping and Handling Cost, Policy [Policy Text Block]

Shipping and handling costs

We include all of the outbound freight, shipping and handling costs associated with the shipment of products to customers in cost of sales. Any amounts paid by customers to us for shipping and handling are recorded in net sales on the consolidated statements of operations.

Inventory, Policy [Policy Text Block]

Inventories

Inventories are valued at the lower of weighted average cost (which approximates computation on a first-in, first-out basis) or market (net realizable value or replacement cost). The valuation of inventory includes the costs for material, labor and manufacturing overhead.

Property, Plant and Equipment, Impairment [Policy Text Block]

Property, plant and equipment.

Property, plant and equipment are recorded at cost or fair market value in the case of the assets acquired through acquisitions, or otherwise at reduced values to the extent there have been asset impairment write-downs. Expenditures for maintenance and repairs are charged directly to expense when incurred, while major improvements are capitalized. Depreciation is computed for financial reporting purposes principally by use of the straight-line method over the following estimated useful lives: machinery and equipment, 3 - 15 years; buildings, 10 - 30 years; and land improvements, 5 - 15 years. Depreciation expense was approximately $10.4 million in 2016, $10.9 million in 2015 and $9.8 million in 2014 and reflected in cost of sales and selling, general and administrative expense (“SG&A expense”) in the consolidated statements of operations. Capitalized software is amortized over the shorter of the estimated useful life or 5 years and reflected in SG&A expense in the consolidated statements of operations. No interest costs were capitalized in 2016, 2015 and 2014.

Goodwill and Intangible Assets, Goodwill, Policy [Policy Text Block]

Goodwill

Goodwill is the excess of cost over the fair value of net assets of businesses acquired. Goodwill is not amortized but is tested annually for impairment and whenever events or circumstances change that would make it more likely than not that an impairment may have occurred. We perform our annual impairment analysis as of the first day of the fourth quarter each year. The evaluation of impairment involves comparing the current estimated fair value of the reporting unit to its recorded value, including goodwill. We perform a qualitative assessment to determine whether it is more likely than not that the fair value of the reporting unit is less than its carrying amount. It may be necessary to perform a quantitative analysis where a discounted cash flow model is used to determine the current estimated fair value of the reporting unit. Key assumptions used to determine the fair value of the reporting unit as part of our annual testing (and any required interim testing) include: (a) expected cash flows for the five-year period following the testing date; (b) an estimated terminal value using a terminal year growth rate based on the growth prospects of the reporting unit; (c) a discount rate based on our estimated after-tax weighted average cost of capital; and (d) a probability-weighted scenario approach by which varying cash flows are assigned to alternative scenarios based on their likelihood of occurrence. In developing these assumptions, we consider historical and anticipated future results, general economic and market conditions, the impact of planned business and operational strategies and all available information at the time the fair value of the reporting unit is estimated. Assumptions in estimating future cash flows are subject to a high degree of judgment and complexity. Changes in assumptions and estimates may affect the fair value of goodwill and could result in impairment charges in future periods.

Based on the results of our impairment analysis, no goodwill impairment losses were recognized in the consolidated statements of operations for 2016

. Subsequent to the analysis, there have been no events or circumstances that indicate any potential impairment of goodwill.

Other Assets [Policy Text Block]

Other assets.

Other assets consist principally of capitalized financing costs and the cash surrender value of life insurance policies. Capitalized financing costs are amortized using the straight-line method, which approximates the effective interest method over the term of the related credit agreement, and reflected in interest expense in the consolidated statements of operations.

Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block]

Long-lived assets

Long-lived assets include property, plant and equipment and identifiable intangible assets with definite useful lives. Finite-lived intangible assets are amortized over their estimated useful lives. Our

intangible assets consist of customer relationships, developed technology and know-how and non-competition agreements that are being amortized on a straight-line basis over their finite useful lives (see Note 7 to the consolidated financial statements). We assess the impairment of long-lived assets whenever events or changes in circumstances indicate that the carrying value may not be fully recoverable. When we determine that the carrying value of such assets may not be recoverable, we measure recoverability based on the undiscounted cash flows expected to be generated by the related asset or asset group. If it is determined that an impairment loss has occurred, the loss is recognized in the period in which it is incurred and is calculated as the difference between the carrying value and the present value of estimated future net cash flows or comparable market values.

During 2016 and 2015, we recorded $20,000 and $0.3 million, respectively, of impairment charges related to long-lived assets resulting from the consolidation of our PC strand operations with the closure of the Newnan, Georgia facility (see Note 5 to the consolidated financial statements). There were no impairment losses in 2014

Fair Value Measurement, Policy [Policy Text Block]

Fair value of financial instruments

The carrying amounts for cash and cash equivalents, accounts receivable, and accounts payable and accrued expenses approximate fair value because of their short maturities.

Income Tax, Policy [Policy Text Block]

Income taxes.

Income taxes are based on pretax financial accounting income. Deferred tax assets and liabilities are recognized for the expected tax consequences of temporary differences between the tax bases of assets and liabilities and their reported amounts. We assess the need to establish a valuation allowance against deferred tax assets to the extent we no longer believe it is more likely than not that the tax assets will be fully realized.

Earnings Per Share, Policy [Policy Text Block]

Earnings per share.

Basic earnings per share (“EPS”) are computed by dividing earnings available to common shareholders

by the weighted average number of shares of common stock outstanding during the period. Diluted EPS are computed by dividing earnings available to common shareholders

by the weighted average number of shares of common stock and other dilutive equity securities outstanding during the period. Securities that have the effect of increasing EPS are considered to be antidilutive and are not included in the computation of diluted EPS.