Atkore (ATKR) 10-Q 7 Aug 19 2019 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Jun. 28, 2019	Jul. 26, 2019
Cover page.
Title of 12(b) Security	Common Stock, $.01 par value per share
Entity Incorporation, State or Country Code	DE
Document Transition Report	false
Document Quarterly Report	true
Entity Registrant Name	Atkore International Group Inc.
Entity Central Index Key	0001666138
Document Type	10-Q
Entity File Number	001-37793
Document Period End Date	Jun. 28, 2019
Document Fiscal Year Focus	2019
Amendment Flag	false
Document Fiscal Period Focus	Q3
Document Fiscal Year Focus	--09-30
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		46,819,639
Entity Tax Identification Number	90-0631463
Entity Address, Address Line One	16100 South Lathrop Avenue
Entity Address, City or Town	Harvey
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60426
City Area Code	708
Local Phone Number	339-1610
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
Trading Symbol	ATKR
Security Exchange Name	NYSE

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 28, 2019	Jun. 29, 2018	Jun. 28, 2019	Jun. 29, 2018
Income Statement [Abstract]
Net sales	$ 493,491	$ 498,014	$ 1,414,828	$ 1,357,572
Cost of sales	367,357	377,685	1,061,350	1,031,219
Gross profit	126,134	120,329	353,478	326,353
Selling, general and administrative	59,049	57,482	171,778	169,195
Intangible asset amortization	7,868	7,694	24,278	24,146
Operating income	59,217	55,153	157,422	133,012
Interest expense, net	12,789	12,442	38,277	28,322
Other (income) expense, net	(1,228)	(1,840)	(3,422)	(27,516)
Income before income taxes	47,656	44,551	122,567	132,206
Income tax expense	11,106	10,352	29,513	28,260
Net income	$ 36,550	$ 34,199	$ 93,054	$ 103,946
Net income per share
Basic (in dollars per share)	$ 0.77	$ 0.73	$ 1.95	$ 1.92
Diluted (in dollars per share)	$ 0.75	$ 0.70	$ 1.90	$ 1.84

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 28, 2019	Jun. 29, 2018	Jun. 28, 2019	Jun. 29, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 36,550	$ 34,199	$ 93,054	$ 103,946
Other comprehensive (loss) income , net of tax:
Change in foreign currency translation adjustment	(610)	(3,293)	(2,404)	(1,793)
Change in unrecognized loss related to pension benefit plans	20	65	60	194
Total other comprehensive (loss)	(590)	(3,228)	(2,344)	(1,599)
Comprehensive income	$ 35,960	$ 30,971	$ 90,710	$ 102,347

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 28, 2019	Sep. 30, 2018
Current Assets:
Cash and cash equivalents	$ 100,734	$ 126,662
Accounts receivable, less allowance for doubtful accounts of $1,448 and $1,762, respectively	322,156	265,147
Inventories, net	224,771	221,753
Prepaid expenses and other current assets	43,225	33,576
Total current assets	690,886	647,138
Property, plant and equipment, net	237,565	213,108
Intangible assets, net	291,188	291,916
Goodwill	189,050	170,129
Deferred tax assets	1,074	162
Other long-term assets	3,251	1,607
Total Assets	1,413,014	1,324,060
Current Liabilities:
Short-term debt and current maturities of long-term debt	0	26,561
Accounts payable	152,898	156,525
Income tax payable	1,082	542
Accrued compensation and employee benefits	29,153	33,350
Customer liabilities	42,922	3,377
Other current liabilities	42,963	52,392
Total current liabilities	269,018	272,747
Long-term debt	884,503	877,686
Deferred tax liabilities	26,749	16,510
Other long-term tax liabilities	894	1,443
Pension liabilities	15,068	17,075
Other long-term liabilities	14,264	16,540
Total Liabilities	1,210,496	1,202,001
Equity:
Common stock, $0.01 par value, 1,000,000,000 shares authorized, 46,676,788 and 47,079,645 shares issued and outstanding, respectively	468	472
Treasury stock, held at cost, 260,900 and 260,900 shares, respectively	(2,580)	(2,580)
Additional paid-in capital	472,138	457,978
Accumulated deficit	(246,393)	(317,373)
Accumulated other comprehensive loss	(21,115)	(16,438)
Total Equity	202,518	122,059
Total Liabilities and Equity	$ 1,413,014	$ 1,324,060

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Jun. 28, 2019	Sep. 30, 2018
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 1,448	$ 1,762
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (shares)	1,000,000,000	1,000,000,000
Common stock, shares issued (shares)	46,676,788	47,079,645
Common stock, shares outstanding (shares)	46,676,788	47,079,645
Treasury stock (shares)	260,900	260,900

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Jun. 28, 2019	Jun. 29, 2018
Operating activities:
Net income	$ 93,054	$ 103,946
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	54,061	49,255
Deferred income taxes	1,882	(4,354)
Gain on sale of a business	0	(27,575)
Stock-based compensation	8,936	9,828
Other adjustments to net income	3,857	4,642
Changes in operating assets and liabilities, net of effects from acquisitions
Accounts receivable	(4,190)	(40,160)
Inventories	5,032	(18,038)
Accounts payable	(11,218)	29,420
Other, net	(31,235)	13,614
Net cash provided by operating activities	120,179	120,578
Investing activities:
Capital expenditures	(21,611)	(26,314)
Divestiture of business	0	42,631
Acquisition of businesses, net of cash acquired	(83,385)	(3,350)
Other, net	(194)	1,475
Net cash (used in) provided by investing activities	(105,190)	14,442
Financing activities:
Borrowings under credit facility	39,000	309,000
Repayments under credit facility	(39,000)	(394,000)
Repayments of short-term debt	(20,980)	(5,850)
Repayments of long-term debt	0	(1,217)
Issuance of long-term debt	0	426,217
Payment for debt financing costs and fees	0	(5,801)
Issuance of common stock	5,232	10,874
Repurchase of common stock	(24,419)	(410,157)
Other, net	(105)	(114)
Net cash used for financing activities	(40,272)	(71,048)
Effects of foreign exchange rate changes on cash and cash equivalents	(645)	(171)
(Decrease) increase in cash and cash equivalents	(25,928)	63,801
Cash and cash equivalents at beginning of period	126,662	45,718
Cash and cash equivalents at end of period	100,734	109,519
Supplementary Cash Flow information
Capital expenditures, not yet paid	$ 767	$ 363

Condensed Consolidated Statem_4

Condensed Consolidated Statement of Changes Shareholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Balance at beginning of period (in shares) at Sep. 30, 2017		63,305
Balance at beginning of period at Sep. 30, 2017	$ 360,871	$ 634	$ (2,580)	$ 423,232	$ (42,433)	$ (17,982)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	27,189				27,189
Other comprehensive (loss) income	396					396
Stock-based compensation	3,564			3,564
Issuance of common stock (in shares)		565
Issuance of common stock	3,328	$ 6		3,322
Repurchase of common stock (in shares)		(351)
Repurchase of common stock	(6,680)	$ (4)			(6,676)
Balance at end of period (in shares) at Dec. 29, 2017		63,519
Balance at end of period at Dec. 29, 2017	388,668	$ 636	(2,580)	430,118	(21,920)	(17,586)
Balance at beginning of period (in shares) at Sep. 30, 2017		63,305
Balance at beginning of period at Sep. 30, 2017	360,871	$ 634	(2,580)	423,232	(42,433)	(17,982)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	103,946
Other comprehensive (loss) income	(1,599)
Balance at end of period (in shares) at Jun. 29, 2018		45,972
Balance at end of period at Jun. 29, 2018	73,763	$ 461	(2,580)	443,918	(348,455)	(19,581)
Balance at beginning of period (in shares) at Dec. 29, 2017		63,519
Balance at beginning of period at Dec. 29, 2017	388,668	$ 636	(2,580)	430,118	(21,920)	(17,586)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	42,558				42,558
Other comprehensive (loss) income	1,233					1,233
Stock-based compensation	2,770			2,770
Issuance of common stock (in shares)		291
Issuance of common stock	1,971	$ 3		1,968
Repurchase of common stock (in shares)		(17,232)
Repurchase of common stock	(375,125)	$ (172)			(374,953)
Balance at end of period (in shares) at Mar. 30, 2018		46,578
Balance at end of period at Mar. 30, 2018	62,075	$ 467	(2,580)	434,856	(354,315)	(16,353)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	34,199				34,199
Other comprehensive (loss) income	(3,228)					(3,228)
Stock-based compensation	3,494			3,494
Issuance of common stock (in shares)		753
Issuance of common stock	5,575	$ 7		5,568
Repurchase of common stock (in shares)		(1,359)
Repurchase of common stock	(28,352)	$ (13)			(28,339)
Balance at end of period (in shares) at Jun. 29, 2018		45,972
Balance at end of period at Jun. 29, 2018	73,763	$ 461	(2,580)	443,918	(348,455)	(19,581)
Balance at beginning of period (in shares) at Sep. 30, 2018		47,080
Balance at beginning of period at Sep. 30, 2018	122,059	$ 472	(2,580)	457,978	(317,373)	(16,438)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	26,949				26,949
Other comprehensive (loss) income	(2,721)					(2,721)
Stock-based compensation	2,982			2,982
Issuance of common stock (in shares)		131
Issuance of common stock	(695)	$ 1		(696)
Repurchase of common stock (in shares)		(1,230)
Repurchase of common stock	(24,419)	$ (12)			(24,407)
Balance at end of period (in shares) at Dec. 28, 2018		45,981
Balance at end of period at Dec. 28, 2018	124,155	$ 461	(2,580)	460,264	(314,831)	(19,159)
Balance at beginning of period (in shares) at Sep. 30, 2018		47,080
Balance at beginning of period at Sep. 30, 2018	122,059	$ 472	(2,580)	457,978	(317,373)	(16,438)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	93,054
Other comprehensive (loss) income	(2,344)
Balance at end of period (in shares) at Jun. 28, 2019		46,676
Balance at end of period at Jun. 28, 2019	202,518	$ 468	(2,580)	472,138	(246,393)	(21,115)
Balance at beginning of period (in shares) at Dec. 28, 2018		45,981
Balance at beginning of period at Dec. 28, 2018	124,155	$ 461	(2,580)	460,264	(314,831)	(19,159)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	29,555				29,555
Other comprehensive (loss) income	967					967
Reclassification of Stranded Tax Benefits	0				2,333	(2,333)
Stock-based compensation	1,834			1,834
Issuance of common stock (in shares)		235
Issuance of common stock	1,986	$ 2		1,984
Balance at end of period (in shares) at Mar. 29, 2019		46,216
Balance at end of period at Mar. 29, 2019	158,497	$ 463	(2,580)	464,082	(282,943)	(20,525)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	36,550				36,550
Other comprehensive (loss) income	(590)					(590)
Reclassification of Stranded Tax Benefits					2,333
Stock-based compensation	4,120			4,120
Issuance of common stock (in shares)		460
Issuance of common stock	3,941	$ 5		3,936
Balance at end of period (in shares) at Jun. 28, 2019		46,676
Balance at end of period at Jun. 28, 2019	$ 202,518	$ 468	$ (2,580)	$ 472,138	$ (246,393)	$ (21,115)

Basis of Presentation and Summa

Basis of Presentation and Summary of Significant Accounting Policies	9 Months Ended
	Jun. 28, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and Summary of Significant Accounting Policies	1. BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation Organization and Ownership Structure — Atkore International Group Inc. (the "Company", "Atkore" or "AIG") is a leading manufacturer of Electrical Raceway products primarily for the non-residential construction and renovation markets and Mechanical Products & Solutions (" MP&S ") for the construction and industrial markets. Electrical Raceway products form the critical infrastructure that enables the deployment, isolation and protection of a structure's electrical circuitry from the original power source to the final outlet. MP&S frame, support and secure component parts in a broad range of structures, equipment and systems in electrical, industrial and construction applications. Atkore was incorporated in the State of Delaware on November 4, 2010. Atkore is the sole stockholder of Atkore International Holdings Inc. ("AIH"), which in turn is the sole stockholder of Atkore International, Inc. ("AII"). Basis of Presentation — The accompanying unaudited condensed consolidated financial statements of the Company included herein have been prepared in accordance with accounting principles generally accepted in the United States of America ("GAAP"). These unaudited condensed consolidated financial statements have been prepared in accordance with the Company's accounting policies and on the same basis as those financial statements included in the Company's latest Annual Report on Form 10-K for the year ended September 30, 2018 filed with the U.S. Securities and Exchange Commission (the "SEC") on November 28, 2018, and should be read in conjunction with those consolidated financial statements and the notes thereto. Certain information and disclosures normally included in the Company's annual financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to the rules and regulations of the SEC. The unaudited condensed consolidated financial statements include the assets and liabilities used in operating the Company's business. All intercompany balances and transactions have been eliminated in consolidation. The results of companies acquired or disposed of are included in the unaudited condensed consolidated financial statements from the effective date of acquisition or up to the date of disposal. These statements include all adjustments (consisting of normal recurring adjustments) that the Company considered necessary to present a fair statement of its results of operations, financial position and cash flows. The results reported in these unaudited condensed consolidated financial statements should not be regarded as necessarily indicative of results that may be expected for the entire year. Fiscal Periods — The Company has a fiscal year that ends on September 30. It is the Company's practice to establish quarterly closings using a 4-5-4 calendar. The Company's fiscal quarters end on the last Friday in December, March and June. Use of Estimates — The preparation of the condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclose contingent assets and liabilities at the date of the condensed consolidated financial statements and report the associated amounts of revenues and expenses. Actual results could differ materially from these estimates. Summary of Significant Accounting Policies Fair Value Measurements — Authoritative guidance for fair value measurements establishes a three-level hierarchy that ranks the quality and reliability of information used in developing fair value estimates. The hierarchy gives the highest priority to quoted prices in active markets and the lowest priority to unobservable data. In cases where two or more levels of inputs are used to determine fair value, a financial instrument’s level is determined based on the lowest level input that is considered significant to the fair value measurement in its entirety. The three levels of the fair value hierarchy are summarized as follows: Level 1 — inputs are based upon quoted prices (unadjusted) in active markets for identical assets or liabilities that are accessible as of the measurement date. Level 2 — inputs are based upon quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, and model-derived valuations for the asset or liability that are derived principally from or corroborated by market data for which the primary inputs are observable, including forward interest rates, yield curves, credit risk and exchange rates. Level 3 — inputs for the valuations are unobservable and are based on management’s estimates of assumptions that market participants would use in pricing the asset or liability. The fair values are therefore determined using model-based techniques such as option pricing models and discounted cash flow models. See Note 15, ''Fair Value Measurements'' for further detail. Recent Accounting Pronouncements A summary of recently adopted accounting guidance is as follows. Adoption dates are on the first day of the fiscal year indicated below, unless otherwise specified. ASU Description of ASU Impact to Atkore Note Adoption Date 2014-09 Revenue from Contracts with Customers and subsequent amendments The Accounting Standards Update ("ASU") provides guidance for revenue recognition. The update's core principle is that a company will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. In doing so, companies will need to use more judgment and make more estimates than under current guidance. Examples of the use of judgments and estimates may include identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. The update also requires more detailed disclosures to enable users of financial statements to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. The update provides for two transition methods to the new guidance: a full retrospective approach and a modified retrospective approach. The Company adopted the guidance in the first quarter of 2019 using the modified retrospective method. See Note 2, "Revenue from Contracts with Customers" for further detail. 2 2019 2018-02 Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income The ASU provided entities with the option to reclassify tax effects stranded in accumulated other comprehensive income as a result of the "H.R.1", also known as the "Tax Cuts and Jobs Act" ("TCJA") to retained earnings. The Company elected to adopt the guidance early in the quarter ended March 29, 2019. As a result of adoption of the ASU, the Company reclassified $2,333 of stranded tax benefits related to its pension plans out of Accumulated other comprehensive loss and into Accumulated deficit for the quarter ended March 29, 2019. The Company's policy is to release the tax effects as the related amounts in other comprehensive income are recognized in net income. 10 2019 2018-07 Improvements to Nonemployee Share-Based Payment Accounting. The ASU simplifies the accounting for share-based payments to nonemployees by aligning it with the accounting for share-based payments to employees, with certain exceptions. The Company elected to adopt the guidance early in the quarter ended June 28, 2019. There was no material impact to the consolidated financial statements as a result of the adoption of ASU 2018-07. 2019 2018-13 Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement The ASU amends Accounting Standard Codification ("ASC") 820 to add, remove and clarify disclosure requirements related to fair value measurements. The Company elected to adopt the guidance early in the quarter ended June 28, 2019. There was no material impact to the consolidated financial statements as a result of the adoption of ASU 2018-13. 2019 A summary of accounting guidance not yet adopted is as follows. Effective dates are on the first day of the fiscal year indicated below, unless otherwise specified. ASU Description of ASU Impact to Atkore Effective Date 2016-02 Leases (Topic 842) The ASU requires companies to use a "right of use" lease model that assumes that each lease creates an asset (the lessee's right to use the leased asset) and a liability (the future rent payment obligations), which should be reflected on a lessee's balance sheet to fairly represent the lease transaction and the lessee's related financial obligations with terms of more than 12 months. The Company will adopt the new lease guidance in the first quarter of fiscal 2020. The Company has established an implementation team, deployed lease landscape surveys, selected a software provider, completed lease data abstraction, progressed on software implementation and is currently evaluating the impact of adoption of this ASU on its consolidated financial statements. 2020 2016-13 Financial Instruments - Credit Losses (Topic 326) The ASU adds to U.S. GAAP an impairment model (known as the current expected credit loss (CECL) model) that is based on expected losses rather than incurred losses. Under the new guidance, an entity recognizes as an allowance its estimate of expected credit losses, which the FASB believes will result in more timely recognition of such losses. Under evaluation. 2021 2018-14 Disclosure Framework - Changes to the Disclosure Requirements for Defined Benefit Plans The ASU amends ASC 715 to add, remove and clarify disclosure requirements related to defined benefit pension and other postretirement plans. Under evaluation. 2021

Revenue from Contracts with Cus

Revenue from Contracts with Customers	9 Months Ended
	Jun. 28, 2019
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Customers	2. REVENUE FROM CONTRACTS WITH CUSTOMERS In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers, and issued subsequent amendments to the initial guidance in August 2015, March 2016, April 2016, May 2016, and December 2016 within ASU 2015-14, ASU 2016-08, ASU 2016-10 and ASU 2016-20, respectively. The core principle of this new revenue recognition guidance is that a company will recognize revenue when promised goods or services are transferred to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. The new guidance defines a five-step process to implement this core principle. The new guidance also requires more detailed disclosures to enable users of financial statements to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. The new guidance provides for two transition methods, a full retrospective approach and a modified retrospective approach. The Company adopted the new guidance on October 1, 2018 utilizing the modified retrospective method of adoption for contracts not completed at the adoption date and determined there were no changes required to its reported revenues and earnings as a result of the adoption. The impacts to the consolidated financial statements consist of balance sheet reclassifications including amounts associated with the changes in the classification of reserves related to volume rebates and returns reserves. The Company has also enhanced its disclosures of revenue to comply with the new guidance. The impact to the Company’s financial statements as of June 28, 2019 was as follows: As of June 28, 2019 Balance Sheet As Reported Balances before adoption of ASC 606 Effect of Adoption Higher/(Lower) Accounts receivable, net 322,156 283,482 38,674 Customer liabilities 42,922 4,248 38,674 The Company’s revenue arrangements primarily consist of a single performance obligation to transfer promised goods which is satisfied at a point in time when title, risks and rewards of ownership, and subsequently control have transferred to the customer. This generally occurs when the product is shipped to the customer, with an immaterial amount of transactions in which control transfers upon delivery. The Company primarily offers assurance-type standard warranties that do not represent separate performance obligations. The Company has certain arrangements that require it to estimate at the time of sale the amounts of variable consideration that should not be recorded as revenue as certain amounts are not expected to be collected from customers, as well as an estimate of the value of products to be returned. The Company principally relies on historical experience, specific customer agreements, and anticipated future trends to estimate these amounts at the time of sale and to reduce the transaction price. These arrangements include sales discounts and allowances, volume rebates, and returned goods. As part of the adoption of the new revenue standard, the Company has elected to utilize certain practical expedients. The Company records amounts billed to customers for reimbursement of shipping and handling costs within revenue. Shipping and handling costs associated with outbound freight after control over a product has transferred to a customer are accounted for as fulfillment costs and are included in cost of goods sold. Sales taxes and other usage-based taxes are excluded from revenue. The practical expedient not to disclose information about remaining performance obligations has also been elected as these obligations have an original duration of one year or less. The Company does not evaluate whether the selling price includes a financing interest component for contracts that are less than a year. The Company also expenses costs incurred to obtain a contract, primarily sales commissions, as all obligations will be settled in less than one year. The Company typically receives payment 30 to 60 days from the point it has satisfied the related performance obligation. See Note 18, ''Segment Information'' for revenue disaggregated by geography and product categories.

Acquisitions

Acquisitions	9 Months Ended
	Jun. 28, 2019
Business Combinations [Abstract]
Acquisitions	3. ACQUISITIONS From time to time, the Company enters into strategic acquisitions in an effort to better service existing customers and to attain new customers. On June 3, 2019, the Company acquired the assets of United Structural Products, LLC, a manufacturer of welded aluminum and engineered-to-order cable trays, for a purchase price of $25,486 , net of cash received. The condensed consolidated financial statements include the results of the acquired company from the acquisition date. Net sales and net income of the acquired company included in the condensed consolidated statement of operations for the three and nine months ended June 28, 2019 , were insignificant. As a result of the acquisition, the Company recognized $10,137 of goodwill, $11,937 of identifiable intangible assets and $3,412 of working capital and other net other tangible assets. As of June 28, 2019 , the purchase price allocation has not been finalized as the Company is finalizing working capital, intangible asset and fixed asset fair values. On October 1, 2018, the Company acquired all of the outstanding stock of Vergokan International NV ("Vergokan") for a purchase price of $57,899 , net of cash received. Vergokan is a leading manufacturer of cable tray and cable ladder systems, underfloor installations and industrial floor trunking that serves industrial, power and energy, commercial and infrastructure sectors in more than 45 countries. This transaction provides Atkore with an expanded presence in Western Europe and strengthens the Company's electrical portfolio of cable management products within the Electrical Raceway segment. The Company incurred approximately $148 for acquisition-related expenses for Vergokan which were recorded as a component of selling, general and administrative expenses for the nine months ended June 28, 2019 . The Company incurred approximately $ 293 for acquisition-related expenses for Vergokan which were recorded as a component of selling, general and administrative expenses for the three and twelve months ended September 30, 2018. The purchase price was allocated to tangible and intangible assets acquired and liabilities assumed, based on their fair values. The following table summarizes the Level 3 fair values assigned to the net assets acquired and liabilities assumed as of the acquisition date: (in thousands) Vergokan Fair value of consideration transferred: Cash consideration $ 58,728 Fair value of assets acquired and liabilities assumed: Cash 829 Accounts receivable 8,761 Inventories 11,434 Intangible assets 12,621 Fixed assets 32,490 Accounts payable (18,716 ) Other 1,680 Net assets acquired 49,099 Excess purchase price attributed to goodwill acquired $ 9,629 The following table summarizes the fair value of intangible assets as of the acquisition date: Vergokan ($ in thousands) Fair Value Weighted Average Useful Life (Years) Customer relationships $ 10,535 12.0 Other 2,086 9.0 Total intangible assets $ 12,621 The purchase price allocation, intangible asset values and related estimates of useful lives for Vergokan have been finalized as of June 28, 2019 . On January 8, 2018, the Company acquired the assets of Communications Integrators, Inc. ("Cii"), a manufacturer of modular, prefabricated power, voice and data distribution systems located in Tempe, Arizona for a total purchase price, including contingent consideration, of $ 3,997 .

Divestitures

Divestitures	9 Months Ended
	Jun. 28, 2019
Discontinued Operations and Disposal Groups [Abstract]
Divestitures	4. DIVESTITURES On March 30, 2018, the Company sold the assets of FlexHead Industries, Inc. and SprinkFLEX, LLC (together "FlexHead") . The FlexHead businesses manufacture commercial flexible sprinkler head connection products for use in a variety of markets, including for industrial, commercial, cold storage, institutional and clean room applications. The cash consideration received, net assets disposed and resulting gain on sale are as follows: (in thousands) FlexHead Cash consideration $ 42,631 Net assets divested 15,056 Gain on sale of a business $ 27,575 Net assets divested included $2,626 of goodwill. Gain on sale of a business includes a working capital adjustment of $838 recorded as a component of Other (income) expense, net

Postretirement Benefits

Postretirement Benefits	9 Months Ended
	Jun. 28, 2019
Retirement Benefits [Abstract]
Postretirement Benefits	5. POSTRETIREMENT BENEFITS The Company provides pension benefits through a number of noncontributory and contributory defined benefit retirement plans covering eligible U.S. employees. As of September 30, 2017, all defined pension benefit plans were frozen, whereby participants no longer accrue credited service. The net periodic benefit credit was as follows: Three months ended Nine months ended (in thousands) Note June 28, 2019 June 29, 2018 June 28, 2019 June 29, 2018 Interest cost 1,166 1,025 $ 3,498 $ 3,074 Expected return on plan assets (1,593 ) (1,604 ) (4,779 ) (4,811 ) Amortization of actuarial loss 25 86 75 257 Net periodic benefit credit 7 $ (402 ) $ (493 ) $ (1,206 ) $ (1,480 )

Restructuring Charges

Restructuring Charges	9 Months Ended
	Jun. 28, 2019
Restructuring and Related Activities [Abstract]
Restructuring Charges	6. RESTRUCTURING CHARGES The liability for restructuring reserves is included within other current liabilities in the Company's condensed consolidated balance sheets as follows: Electrical Raceway MP&S Other/Corporate (in thousands) Severance (a) Other (a) Severance Other Severance Total Balance as of September 30, 2017 $ 449 $ — $ 278 $ 10 $ — $ 737 Charges 536 1,130 97 179 98 2,040 Utilization (787 ) (820 ) (178 ) (160 ) (98 ) (2,043 ) Reversal — — (191 ) — — (191 ) Exchange rate effects 14 — (6 ) — — 8 Balance as of September 30, 2018 212 310 — 29 — 551 Charges 681 2,500 — — — 3,181 Utilization (806 ) (2,751 ) — (29 ) — (3,586 ) Balance as of June 28, 2019 $ 87 $ 59 $ — $ — $ — $ 146 (a) Primarily related to Atkore's commitment to close certain facilities as part of its continuing effort to realign its strategic focus. The Company recorded severance restructuring charges of $681 and $327 related to termination benefits during the nine months ended June 28, 2019 and June 29, 2018 , respectively. The Company recorded other restructuring charges to close facilities of $2,473 and $600 for the nine months ended June 28, 2019 and June 29, 2018 , respectively. The Company expects to utilize all restructuring accruals as of June 28, 2019 within the next twelve months. The net restructuring charges included as a component of selling, general and administrative expenses in the Company's condensed consolidated statements of operations were as follows: Three months ended Nine months ended (in thousands) June 28, 2019 June 29, 2018 June 28, 2019 June 29, 2018 Total restructuring charges, net $ 709 $ 407 $ 3,181 $ 1,245

Other (Income) Expense, Net

Other (Income) Expense, Net	9 Months Ended
	Jun. 28, 2019
Other Income and Expenses [Abstract]
Other (Income) Expense, Net	7. OTHER (INCOME) EXPENSE, NET Other (income) expense, net consisted of the following: Three months ended Nine months ended (in thousands) June 28, 2019 June 29, 2018 June 28, 2019 June 29, 2018 Gain on sale of a business — (838 ) — (27,575 ) Undesignated foreign currency derivative instruments (2,095 ) (3,757 ) (3,562 ) (22 ) Foreign exchange (gain) loss on intercompany loans 1,360 3,374 1,423 795 Debt modification costs — — — 892 Pension-related benefits (402 ) (493 ) (1,206 ) (1,480 ) Other (91 ) (126 ) (77 ) (126 ) Other (income) expense, net $ (1,228 ) $ (1,840 ) $ (3,422 ) $ (27,516 )

Income Taxes

Income Taxes	9 Months Ended
	Jun. 28, 2019
Income Tax Disclosure [Abstract]
Income Taxes	8. INCOME TAXES On December 22, 2017, " H.R.1 ," also known as the "Tax Cuts and Jobs Act" ("TCJA"), was signed into law. TCJA provides for significant changes to corporate taxation including, but not limited to, a reduction of the federal corporate tax rate from 35% to 21% , limitations on the deductibility of interest expense and executive compensation, full expensing of the costs of qualified property in the period of acquisition, the elimination of the domestic production activities deduction and a new provision designed to tax global intangible low-taxed income ("GILTI"). The legislation also adopted a new quasi-territorial tax regime and imposed a one-time transition tax on deemed repatriated earnings of certain foreign subsidiaries. The value of the Company’s net deferred tax liability on the balance sheet decreased as a result of the enacted tax rates creating a one-time tax benefit to the Company; the preliminary analysis of the impact, using December 29, 2017 values, was an estimated decrease to the net deferred tax liability of $4,758 , which was recognized in the first quarter of fiscal 2018. The SEC Staff Accounting Bulletin No. 118 allowed for a measurement period of up to one year from the date of enactment; during the course of the fiscal year ended September 30, 2018, the Company recorded an adjustment to the re-measurement of deferred tax liabilities of an additional $708 benefit as a result of updated estimates. For the period ended December 28, 2018, the Company finalized the re-measurement with no additional adjustments. The Company has an accumulated earnings and profit deficit in the foreign jurisdictions in which it operates. The Company completed its calculation and did not have an income tax liability from the one-time transition tax on the deemed repatriation of its foreign earnings. The GILTI provision of TCJA requires certain income earned by controlled foreign corporations ("CFCs") to be included currently in the gross income of the CFC's controlling U.S. shareholder. In accordance with accounting standards applicable to income taxes, there is allowed an accounting policy choice of either (1) treating taxes due on U.S. inclusions in taxable income related to GILTI as a current period expense when incurred (the “period cost method”) or (2) factoring such amounts into the Company’s measurement of its deferred taxes (the “deferred method”). The Company has elected the period method and included an estimate of the GILTI tax in the Company’s annualized effective tax rate. For the three months ended June 28, 2019 and June 29, 2018 , the Company's effective tax rate attributable to income before income taxes was 23.3% and 23.2% , respectively. For the three months ended June 28, 2019 and June 29, 2018 , the Company's income tax expense was $11,106 and $10,352 respectively. The increase in the current period effective tax rate was primarily due to the impact of certain nondeductible items as a result of the TCJA. For the nine months ended June 28, 2019 and June 29, 2018 , the Company's effective tax rate attributable to income before income taxes was 24.1% and 21.4% , respectively. For the nine months ended June 28, 2019 and June 29, 2018 , the Company's income tax expense was $29,513 and $28,260 respectively. The increase in the effective tax rate was primarily due to the prior year benefit of the one-time re-measurement of deferred taxes as a result of the TCJA, which was recorded in the first quarter of fiscal 2018. The Company has recorded a valuation allowance against net operating losses in certain foreign jurisdictions. A valuation allowance is recorded when it is determined to be more likely than not that deferred tax assets will not be fully realized in the foreseeable future. The realization of deferred tax assets is dependent upon whether the Company can generate future taxable income of appropriate character in the relevant jurisdiction to utilize the assets. For the nine months ended June 28, 2019 , the Company has fully released a valuation allowance for $550 on deferred tax assets in its Asia Pacific business due to an increase in forecasted taxable income. For the three months ended June 28, 2019 , the Company has released the remaining valuation allowance of $284 on deferred tax assets in its Asia Pacific business due to an increase in forecasted taxable income. The Company recognizes the benefits of uncertain tax positions taken or expected to be taken in tax returns in the provision for income taxes only for those positions that it has determined are more likely than not to be realized upon examination. The Company records interest and penalties related to unrecognized tax benefits as a component of income tax expense. During the nine months ended June 28, 2019 , the balance of unrecognized tax benefits decreased by $549 primarily due to the resolution of a state audit item. During the three months ended June 28, 2019 , the balance of unrecognized tax benefits decreased by an additional $13 . For the nine months ended June 28, 2019 , the Company made no additional provision for U.S. or non-U.S. income taxes for unrecognized deferred tax liabilities for temporary differences related to basis differences in investments in subsidiaries, as the investments are essentially permanent in duration.

Earnings Per Share

Earnings Per Share	9 Months Ended
	Jun. 28, 2019
Earnings Per Share [Abstract]
Earnings Per Share	9. EARNINGS PER SHARE The Company calculates basic and diluted earnings per common share using the two-class method. Under the two-class method, net earnings are allocated to each class of common stock and participating securities as if all of the net earnings for the period had been distributed. The Company's participating securities consist of share-based payment awards that contain a non-forfeitable right to receive dividends and therefore are considered to participate in undistributed earnings with common stockholders. Basic earnings per common share excludes dilution and is calculated by dividing the net earnings allocable to common stock by the weighted-average number of common stock outstanding for the period. Diluted earnings per common share is calculated by dividing net earnings allocated to common stock by the weighted-average number of shares outstanding for the period, as adjusted for the potential dilutive effect of non-participating share-based awards. The following table sets forth the computation of basic and diluted earnings per share: Three months ended Nine months ended (in thousands, except per share data) June 28, 2019 June 29, 2018 June 28, 2019 June 29, 2018 Numerator: Net income $ 36,550 $ 34,199 $ 93,054 $ 103,946 Less: Undistributed earnings allocated to participating securities 996 422 2,499 1,048 Net income available to common shareholders $ 35,554 $ 33,777 $ 90,555 $ 102,898 Denominator: Basic weighted average common shares outstanding 46,386 46,262 46,481 53,592 Effect of dilutive securities: Non-participating employee stock options (1) 1,171 2,150 1,254 2,423 Diluted weighted average common shares outstanding 47,557 48,412 47,735 56,015 Basic earnings per share $ 0.77 $ 0.73 $ 1.95 $ 1.92 Diluted earnings per share $ 0.75 $ 0.70 $ 1.90 $ 1.84 (1) Stock options to purchase approximately 0.3 million and 0.4 million shares of common stock were outstanding during the three months ended June 28, 2019 and June 29, 2018, respectively, but were not included in the calculation of diluted earnings per share as the impact of these options would have been anti-dilutive. Stock options to purchase approximately 0.4 million and 0.4 million shares of common stock were outstanding during the nine months ended June 28, 2019 and June 29, 2018, respectively, but were not included in the calculation of diluted earnings per share as the impact of these options would have been anti-dilutive.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Loss	9 Months Ended
	Jun. 28, 2019
Equity [Abstract]
Accumulated Other Comprehensive Loss	10. ACCUMULATED OTHER COMPREHENSIVE LOSS The following table presents the changes in accumulated other comprehensive loss by component for the nine months ended June 28, 2019 and June 29, 2018 : (in thousands) Defined benefit pension items Currency translation adjustments Total Balance as of September 30, 2018 $ (6,048 ) $ (10,390 ) $ (16,438 ) Other comprehensive loss before reclassifications — (2,404 ) (2,404 ) Amounts reclassified from accumulated other 60 — 60 Net current period other comprehensive income (loss) 60 (2,404 ) (2,344 ) Reclassification of stranded tax benefits (1) (2,333 ) — (2,333 ) Balance as of June 28, 2019 $ (8,321 ) $ (12,794 ) $ (21,115 ) (1) Due to the adoption of ASU 2018-02. (in thousands) Defined benefit pension items Currency translation adjustments Total Balance as of September 30, 2017 $ (10,445 ) $ (7,537 ) $ (17,982 ) Other comprehensive income before reclassifications — (1,793 ) (1,793 ) Amounts reclassified from accumulated other 194 — 194 Net current period other comprehensive income (loss) 194 (1,793 ) (1,599 ) Balance as of June 29, 2018 $ (10,251 ) $ (9,330 ) $ (19,581 ) The following table presents the changes in accumulated other comprehensive loss by component for the three months ended June 28, 2019 and June 29, 2018 : (in thousands) Defined benefit pension items Currency translation adjustments Total Balance as of March 29, 2019 $ (8,341 ) $ (12,184 ) $ (20,525 ) Other comprehensive income before reclassifications — (610 ) (610 ) Amounts reclassified from accumulated other 20 — 20 Net current period other comprehensive income (loss) 20 (610 ) (590 ) Balance as of June 28, 2019 $ (8,321 ) $ (12,794 ) $ (21,115 ) (in thousands) Defined benefit pension items Currency translation adjustments Total Balance as of March 30 2018 $ (10,316 ) $ (6,037 ) $ (16,353 ) Other comprehensive income before reclassifications — (3,293 ) (3,293 ) Amounts reclassified from accumulated other 65 — 65 Net current period other comprehensive income (loss) 65 (3,293 ) (3,228 ) Balance as of June 29, 2018 $ (10,251 ) $ (9,330 ) $ (19,581 )

Inventories, Net

Inventories, Net	9 Months Ended
	Jun. 28, 2019
Inventory Disclosure [Abstract]
Inventories, Net	11. INVENTORIES, NET A majority of the Company's inventories are recorded at the lower of cost (primarily last in, first out, or "LIFO") or market. Approximately 75% and 80% of the Company's inventories were valued at the lower of LIFO cost or market at June 28, 2019 and September 30, 2018 , respectively. Interim LIFO determinations, including those at June 28, 2019 , are based on management's estimates of future inventory levels and costs for the remainder of the current fiscal year. (in thousands) June 28, 2019 September 30, 2018 Purchased materials and manufactured parts, net $ 48,742 $ 58,572 Work in process, net 24,730 21,769 Finished goods, net 151,299 141,412 Inventories, net $ 224,771 $ 221,753 Total inventories would be $15,888 and $26,340 higher than reported as of June 28, 2019 and September 30, 2018 , respectively, if the first-in, first-out method was used for all inventories. As of June 28, 2019 , and September 30, 2018 , the excess and obsolete inventory reserve was $17,099 and $12,909

Property, Plant and Equipment

Property, Plant and Equipment	9 Months Ended
	Jun. 28, 2019
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	12. PROPERTY, PLANT AND EQUIPMENT As of June 28, 2019 , and September 30, 2018 , property, plant and equipment at cost and accumulated depreciation were as follows: (in thousands) June 28, 2019 September 30, 2018 Land $ 19,901 $ 13,295 Buildings and related improvements 122,452 108,758 Machinery and equipment 295,878 262,078 Leasehold improvements 8,347 7,382 Software 24,367 30,502 Construction in progress 17,826 16,777 Property, plant and equipment 488,771 438,792 Accumulated depreciation (251,206 ) (225,684 ) Property, plant and equipment, net $ 237,565 $ 213,108 Depreciation expense for the three months ended June 28, 2019 and June 29, 2018 totaled $9,892 and $8,498 , respectively. Depreciation expense for the nine months ended June 28, 2019 and June 29, 2018 totaled $29,783 and $25,109

Goodwill and Intangible Assets

Goodwill and Intangible Assets	9 Months Ended
	Jun. 28, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	13. GOODWILL AND INTANGIBLE ASSETS Changes in the carrying amount of goodwill are as follows: (in thousands) Electrical Raceway Mechanical Products & Solutions Total Balance as of October 1, 2018 $ 133,566 $ 36,563 $ 170,129 Goodwill acquired during year 19,766 — 19,766 Exchange rate effects (845 ) — (845 ) Balance as of June 28, 2019 $ 152,487 $ 36,563 $ 189,050 Goodwill balances as of October 1, 2018 and June 28, 2019 include $3,924 and $43,000 of accumulated impairment losses within the Electrical Raceway and MP&S segments, respectively. The Company assesses the recoverability of goodwill and indefinite-lived trade names on an annual basis in accordance with ASC 350, "Intangibles - Goodwill and Other." The measurement date is the first day of the fourth fiscal quarter, or more frequently, if events or circumstances indicate that it is more likely than not that the fair value of a reporting unit or the respective indefinite-lived trade name is less than the carrying value. The following table provides the gross carrying value, accumulated amortization and net carrying value for each major class of intangible assets: June 28, 2019 September 30, 2018 ($ in thousands) Weighted Average Useful Life (Years) Gross Carrying Value Accumulated Amortization Net Carrying Value Gross Carrying Value Accumulated Amortization Net Carrying Value Amortizable intangible assets: Customer relationships 11 $ 351,597 $ (164,099 ) $ 187,498 $ 330,295 $ (141,401 ) $ 188,894 Other 8 18,086 (7,276 ) 10,810 16,003 (5,861 ) 10,142 Total 369,683 (171,375 ) 198,308 346,298 (147,262 ) 199,036 Indefinite-lived intangible assets: Trade names 92,880 — 92,880 92,880 — 92,880 Total $ 462,563 $ (171,375 ) $ 291,188 $ 439,178 $ (147,262 ) $ 291,916 Other intangible assets consist of definite-lived trade names, technology, non-compete agreements and backlogs. Amortization expense for the three months ended June 28, 2019 and June 29, 2018 was $7,868 and $7,694 , respectively. Amortization expense for the nine months ended June 28, 2019 and June 29, 2018 was $24,278 and $24,146 , respectively. Expected amortization expense for intangible assets for the remainder of fiscal 2019 and over the next five years and thereafter is as follows: (in thousands) Remaining 2019 $ 9,888 2020 31,581 2021 31,447 2022 30,113 2023 29,993 2024 25,614 Thereafter 39,672 Actual amounts of amortization may differ from estimated amounts due to additional intangible asset acquisitions, impairment of intangible assets and other events.

Debt

Debt	9 Months Ended
	Jun. 28, 2019
Debt Disclosure [Abstract]
Debt	14. DEBT Debt as of June 28, 2019 and September 30, 2018 was as follows: (in thousands) June 28, 2019 September 30, 2018 First Lien Term Loan Facility due December 22, 2023 $ 891,317 $ 912,162 Deferred financing costs (6,976 ) (8,194 ) Other 162 279 Total debt $ 884,503 $ 904,247 Less: Current portion — 26,561 Long-term debt $ 884,503 $ 877,686 The asset-based credit facility (the "ABL Credit Facility") has aggregate commitments of $325,000 and is guaranteed by AIH and the U.S. operating companies owned by AII. AII's availability under the ABL Credit Facility was $312,550 and $315,119 as of June 28, 2019 and September 30, 2018 , respectively. During the three months ended March 29, 2019, the Company made an accelerated repayment of $18,680

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Jun. 28, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	15. FAIR VALUE MEASUREMENTS Certain assets and liabilities are required to be recorded at fair value on a recurring basis. The Company uses forward currency contracts to hedge the effects of foreign exchange relating to certain of the Company’s intercompany balances denominated in a foreign currency. These derivative instruments are not formally designated as hedges by the Company and the terms of these instruments range at inception from six months to six years. Short-term forward currency contracts are recorded in either other current assets or other current liabilities and long-term forward currency contracts are recorded in other long-term liabilities in the condensed consolidated balance sheet. The fair value gains and losses are included in other (income) expense, net within the condensed consolidated statements of operations . See Note 7, ''Other (Income) Expense, net'' for further detail. The total notional amounts of undesignated forward currency contracts were £ 45.0 million and £ 49.1 million as of June 28, 2019 and September 30, 2018 , respectively. Cash flows associated with derivative financial instruments are recognized in the operating section of the condensed consolidated statements of cash flows . The fair value of forward currency contracts is calculated by reference to current forward exchange rates for contracts with similar maturity profiles. The following table presents the Company's assets and liabilities measured at fair value: June 28, 2019 September 30, 2018 (in thousands) Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 Assets Cash equivalents $ 57,089 $ — $ — $ 28,175 $ — $ — Forward currency contracts — 1,686 — — — — Liabilities Forward currency contracts — 87 — — 1,857 — The Company's remaining financial instruments consist primarily of cash, accounts receivable and accounts payable whose carrying value approximate their fair value due to their short-term nature. The estimated fair value of financial instruments not carried at fair value in the condensed consolidated balance sheets were as follows: June 28, 2019 September 30, 2018 (in thousands) Carrying Value Fair Value Carrying Value Fair Value First Lien Term Loan Facility due December 22, 2023 $ 892,120 $ 888,195 $ 913,100 $ 916,113 In determining the approximate fair value of its long-term debt, the Company used the trading values among financial institutions, and these values fall within Level 2 of the fair value hierarchy. The carrying value of the ABL Credit Facility approximates fair value due to it being a market-linked variable rate debt.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Jun. 28, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	16. COMMITMENTS AND CONTINGENCIES The Company has obligations related to commitments to purchase certain goods. As of June 28, 2019 , such obligations were $129,758 for the rest of fiscal year 2019 and $3,317 for fiscal year 2020 and beyond. These amounts represent open purchase orders for materials used in production. Legal Contingencies — The Company is a defendant in a number of pending legal proceedings, some of which were inherited from its former parent, Tyco International Ltd. ("Tyco"), including certain product liability claims. Several lawsuits have been filed against the Company and the Company has also received other claim demand letters alleging that the Company's anti-microbial coated steel sprinkler pipe, which the Company has not manufactured or sold for several years, is incompatible with chlorinated polyvinyl chloride and caused stress cracking in such pipe manufactured by third parties when installed together in the same sprinkler system, which the Company refers to collectively as the " Special Products Claims ." After an analysis of claims experience, the Company reserved its best estimate of the probable and reasonably estimable losses related to these matters. The Company's total product liability reserves were $1,204 and $6,755 as of June 28, 2019 and September 30, 2018 , respectively. As of June 28, 2019 , the Company believes that the range of losses for product liability claims is between $1,000 and $8,000 . During the quarter ended December 28, 2018, Tyco and the Company agreed with a plaintiff to settle one Special Products Claim that was to go to trial. The Company agreed to fund the total settlement in exchange for Tyco's agreement to cap the Company's Special Products Claim deductible at $12,000 , as opposed to the $13,000 cap negotiated within the original indemnity agreement. As of June 28, 2019 , the cap has been satisfied and Tyco, now Johnson Controls International plc, is contractually obligated to indemnify the Company in respect of claims of incompatibility between the Company's antimicrobial coated steel sprinkler pipe and CPVC pipe used in the same sprinkler system. At this time, the Company does not expect the outcome of the Special Products Claims proceedings, either individually or in the aggregate, to have a material adverse effect on its business, financial condition, results of operations or cash flows, and the Company believes that its reserves are adequate for all remaining contingencies for Special Products Claims. In addition to the matters discussed above, from time to time, the Company is subject to a number of disputes, administrative proceedings and other claims arising out of the ordinary conduct of the Company's business. These matters generally relate to disputes arising out of the use or installation of the Company's products, product liability litigation, contract disputes, patent infringement accusations, employment matters, personal injury claims and similar matters. On the basis of information currently available to the Company, it does not believe that existing proceedings and claims will have a material adverse effect on its business, financial condition, results of operations or cash flows. However, litigation is unpredictable, and the Company could incur judgments or enter into settlements for current or future claims that could adversely affect its business, financial condition, results of operations or cash flows.

Guarantees

Guarantees	9 Months Ended
	Jun. 28, 2019
Guarantees [Abstract]
Guarantees	17. GUARANTEES The Company had outstanding letters of credit totaling $10,501 supporting workers' compensation and general liability insurance policies as of June 28, 2019 . The Company also had surety bonds primarily related to performance guarantees on supply agreements and construction contracts, and payment of duties and taxes totaling $21,408 as of June 28, 2019 . In disposing of assets or businesses, the Company often provides representations, warranties and indemnities to cover various risks including unknown damage to the assets, environmental risks involved in the sale of real estate, liability to investigate and remediate environmental contamination at waste disposal sites and manufacturing facilities, and unidentified tax liabilities and legal fees related to periods prior to disposition. The Company does not have the ability to estimate the potential liability from such indemnities because they relate to unknown conditions. However, the Company has no reason to believe that these uncertainties would have a material adverse effect on the Company's business, financial condition, results of operations or cash flows. In the normal course of business, the Company is liable for product performance and contract completion. In the opinion of management, such obligations will not have a material adverse effect on the Company's business, financial condition, results of operations or cash flows.

Segment Information

Segment Information	9 Months Ended
	Jun. 28, 2019
Segment Reporting [Abstract]
Segment Information	18. SEGMENT INFORMATION The Company has two operating segments, which are also its reportable segments. The Company's operating segments are organized based upon primary market channels and, in most instances, the end use of products. Through its Electrical Raceway segment, the Company manufactures products that deploy, isolate and protect a structure's electrical circuitry from the original power source to the final outlet. These products, which include electrical conduit, armored cable, cable trays, mounting systems and fittings, are critical components of the electrical infrastructure for maintenance, repair and remodel markets. The vast majority of the Company's Electrical Raceway net sales are made to electrical distributors, who then serve electrical contractors and the Company considers both to be customers. Through the MP&S segment, the Company provides products and services that frame, support and secure component parts in a broad range of structures, equipment and systems in electrical, industrial and construction applications. The Company's principal products in this segment are metal framing products and in-line galvanized mechanical tube. Through its metal framing business, the Company designs, manufactures and installs metal strut and fittings used to assemble mounting structures that support heavy equipment and electrical content in buildings and other structures. Both segments use Adjusted EBITDA as the primary measure of profit and loss. Segment Adjusted EBITDA is the sum of income (loss) from operations before income taxes, adjusted to exclude unallocated expenses, depreciation and amortization, interest expense, net, gain (loss) on extinguishment of debt, restructuring and impairments, stock-based compensation, certain legal matters, transaction costs and other items, such as inventory reserves and adjustments, release of indemnified uncertain tax positions, and the impact of foreign exchange gains or losses. Intersegment transactions primarily consist of product sales at designated transfer prices on an arm's-length basis. Gross profit earned and reported within the segment is eliminated in the Company's consolidated results. Certain manufacturing and distribution expenses are allocated between the segments on a pro rata basis due to the shared nature of activities. Recorded amounts represent a proportional amount of the quantity of product produced for each segment. Certain assets, such as machinery and equipment and facilities, are not allocated to each segment despite serving both segments. These shared assets are reported within the MP&S segment. We allocate certain corporate operating expenses that directly benefit our operating segments, such as insurance and information technology, on a basis that reasonably approximates an estimate of the use of these services. Three months ended June 28, 2019 June 29, 2018 (in thousands) External Net Sales Intersegment Sales Adjusted EBITDA External Net Sales Intersegment Sales Adjusted EBITDA Electrical Raceway $ 372,895 $ 334 $ 76,721 $ 369,812 $ 521 $ 74,461 MP&S 120,596 — 20,595 128,202 37 12,013 Eliminations — (334 ) — (558 ) Consolidated operations $ 493,491 $ — $ 498,014 $ — Nine months ended June 28, 2019 June 29, 2018 (in thousands) External Net Sales Intersegment Sales Adjusted EBITDA External Net Sales Intersegment Sales Adjusted EBITDA Electrical Raceway $ 1,069,229 $ 920 $ 212,585 $ 1,010,523 $ 1,120 $ 187,025 MP&S 345,599 — 48,903 347,049 74 39,544 Eliminations — (920 ) — (1,194 ) Consolidated operations $ 1,414,828 $ — $ 1,357,572 $ — Presented below is a reconciliation of operating segment Adjusted EBITDA to Income before income taxes : Three months ended Nine months ended (in thousands) June 28, 2019 June 29, 2018 June 28, 2019 June 29, 2018 Operating segment Adjusted EBITDA Electrical Raceway $ 76,721 $ 74,461 $ 212,585 $ 187,025 MP&S 20,595 12,013 48,903 39,544 Total 97,316 86,474 261,488 226,569 Unallocated expenses (a) (8,835 ) (9,810 ) (25,890 ) (26,077 ) Depreciation and amortization (17,760 ) (16,192 ) (54,061 ) (49,255 ) Interest expense, net (12,789 ) (12,442 ) (38,277 ) (28,322 ) Restructuring and impairments (709 ) (407 ) (3,181 ) (1,245 ) Stock-based compensation (4,120 ) (3,494 ) (8,936 ) (9,828 ) Certain legal matters — — — (2,286 ) Transaction costs (76 ) (768 ) (363 ) (2,676 ) Gain on sale of a business — 838 — 27,575 Other (b) (5,371 ) 352 (8,213 ) (2,249 ) Income before income taxes $ 47,656 $ 44,551 $ 122,567 $ 132,206 (a) Represents unallocated selling, general and administrative activities and associated expenses including, in part, executive, legal, finance, human resources, information technology, business development and communications, as well as certain costs and earnings of employee-related benefits plans, such as stock-based compensation and a portion of self-insured medical costs. (b) Represents other items, such as inventory reserves and adjustments, release of indemnified uncertain tax positions and the impact of foreign exchange gains or losses. The Company's net sales by geography were as follows for the three and nine months ended June 28, 2019 and June 29, 2018 : Three months ended Nine months ended (in thousands) June 28, 2019 June 29, 2018 June 28, 2019 June 29, 2018 United States $ 436,767 $ 449,907 $ 1,240,402 $ 1,222,573 Other Americas 7,821 11,938 26,030 29,653 Europe 36,277 23,822 108,947 67,507 Asia-Pacific 12,626 12,347 39,449 37,839 Total $ 493,491 $ 498,014 $ 1,414,828 $ 1,357,572 The table below shows the amount of net sales from external customers for each of the Company's product categories which accounted for 10% or more of consolidated net sales in either period for the three and nine months ended June 28, 2019 and June 29, 2018 : Three months ended Nine months ended (in thousands) June 28, 2019 June 29, 2018 June 28, 2019 June 29, 2018 Metal Electrical Conduit and Fittings $ 139,342 $ 146,497 $ 404,720 375,507 Armored Cable and Fittings 90,891 84,686 263,864 253,727 PVC Electrical Conduit and Fittings 78,765 86,742 213,181 234,101 Cable Tray and Cable Ladders 50,680 37,715 147,592 108,814 Other raceway products 13,217 14,172 39,872 38,374 Electrical Raceway 372,895 369,812 1,069,229 1,010,523 Mechanical Pipe 63,502 71,756 186,209 182,268 Metal Framing and Fittings 29,328 31,234 88,389 83,544 Other MP&S products 27,766 25,212 71,001 71,854 Impact of Fence and Sprinkler — — — 9,383 MP&S 120,596 128,202 345,599 347,049 Net sales $ 493,491 $ 498,014 $ 1,414,828 $ 1,357,572

Basis of Presentation and Sum_2

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Jun. 28, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation — The accompanying unaudited condensed consolidated financial statements of the Company included herein have been prepared in accordance with accounting principles generally accepted in the United States of America ("GAAP"). These unaudited condensed consolidated financial statements have been prepared in accordance with the Company's accounting policies and on the same basis as those financial statements included in the Company's latest Annual Report on Form 10-K for the year ended September 30, 2018 filed with the U.S. Securities and Exchange Commission (the "SEC") on November 28, 2018, and should be read in conjunction with those consolidated financial statements and the notes thereto. Certain information and disclosures normally included in the Company's annual financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to the rules and regulations of the SEC. The unaudited condensed consolidated financial statements include the assets and liabilities used in operating the Company's business. All intercompany balances and transactions have been eliminated in consolidation. The results of companies acquired or disposed of are included in the unaudited condensed consolidated financial statements from the effective date of acquisition or up to the date of disposal. These statements include all adjustments (consisting of normal recurring adjustments) that the Company considered necessary to present a fair statement of its results of operations, financial position and cash flows. The results reported in these unaudited condensed consolidated financial statements should not be regarded as necessarily indicative of results that may be expected for the entire year.
Fiscal Periods	Fiscal Periods — The Company has a fiscal year that ends on September 30. It is the Company's practice to establish quarterly closings using a 4-5-4 calendar. The Company's fiscal quarters end on the last Friday in December, March and June.
Use of Estimates	Use of Estimates — The preparation of the condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclose contingent assets and liabilities at the date of the condensed consolidated financial statements and report the associated amounts of revenues and expenses. Actual results could differ materially from these estimates.
Fair Value Measurements	Fair Value Measurements — Authoritative guidance for fair value measurements establishes a three-level hierarchy that ranks the quality and reliability of information used in developing fair value estimates. The hierarchy gives the highest priority to quoted prices in active markets and the lowest priority to unobservable data. In cases where two or more levels of inputs are used to determine fair value, a financial instrument’s level is determined based on the lowest level input that is considered significant to the fair value measurement in its entirety. The three levels of the fair value hierarchy are summarized as follows: Level 1 — inputs are based upon quoted prices (unadjusted) in active markets for identical assets or liabilities that are accessible as of the measurement date. Level 2 — inputs are based upon quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, and model-derived valuations for the asset or liability that are derived principally from or corroborated by market data for which the primary inputs are observable, including forward interest rates, yield curves, credit risk and exchange rates. Level 3 — inputs for the valuations are unobservable and are based on management’s estimates of assumptions that market participants would use in pricing the asset or liability. The fair values are therefore determined using model-based techniques such as option pricing models and discounted cash flow models.
Recent Accounting Pronouncements	Recent Accounting Pronouncements A summary of recently adopted accounting guidance is as follows. Adoption dates are on the first day of the fiscal year indicated below, unless otherwise specified. ASU Description of ASU Impact to Atkore Note Adoption Date 2014-09 Revenue from Contracts with Customers and subsequent amendments The Accounting Standards Update ("ASU") provides guidance for revenue recognition. The update's core principle is that a company will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. In doing so, companies will need to use more judgment and make more estimates than under current guidance. Examples of the use of judgments and estimates may include identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. The update also requires more detailed disclosures to enable users of financial statements to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. The update provides for two transition methods to the new guidance: a full retrospective approach and a modified retrospective approach. The Company adopted the guidance in the first quarter of 2019 using the modified retrospective method. See Note 2, "Revenue from Contracts with Customers" for further detail. 2 2019 2018-02 Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income The ASU provided entities with the option to reclassify tax effects stranded in accumulated other comprehensive income as a result of the "H.R.1", also known as the "Tax Cuts and Jobs Act" ("TCJA") to retained earnings. The Company elected to adopt the guidance early in the quarter ended March 29, 2019. As a result of adoption of the ASU, the Company reclassified $2,333 of stranded tax benefits related to its pension plans out of Accumulated other comprehensive loss and into Accumulated deficit for the quarter ended March 29, 2019. The Company's policy is to release the tax effects as the related amounts in other comprehensive income are recognized in net income. 10 2019 2018-07 Improvements to Nonemployee Share-Based Payment Accounting. The ASU simplifies the accounting for share-based payments to nonemployees by aligning it with the accounting for share-based payments to employees, with certain exceptions. The Company elected to adopt the guidance early in the quarter ended June 28, 2019. There was no material impact to the consolidated financial statements as a result of the adoption of ASU 2018-07. 2019 2018-13 Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement The ASU amends Accounting Standard Codification ("ASC") 820 to add, remove and clarify disclosure requirements related to fair value measurements. The Company elected to adopt the guidance early in the quarter ended June 28, 2019. There was no material impact to the consolidated financial statements as a result of the adoption of ASU 2018-13. 2019 A summary of accounting guidance not yet adopted is as follows. Effective dates are on the first day of the fiscal year indicated below, unless otherwise specified. ASU Description of ASU Impact to Atkore Effective Date 2016-02 Leases (Topic 842) The ASU requires companies to use a "right of use" lease model that assumes that each lease creates an asset (the lessee's right to use the leased asset) and a liability (the future rent payment obligations), which should be reflected on a lessee's balance sheet to fairly represent the lease transaction and the lessee's related financial obligations with terms of more than 12 months. The Company will adopt the new lease guidance in the first quarter of fiscal 2020. The Company has established an implementation team, deployed lease landscape surveys, selected a software provider, completed lease data abstraction, progressed on software implementation and is currently evaluating the impact of adoption of this ASU on its consolidated financial statements. 2020 2016-13 Financial Instruments - Credit Losses (Topic 326) The ASU adds to U.S. GAAP an impairment model (known as the current expected credit loss (CECL) model) that is based on expected losses rather than incurred losses. Under the new guidance, an entity recognizes as an allowance its estimate of expected credit losses, which the FASB believes will result in more timely recognition of such losses. Under evaluation. 2021 2018-14 Disclosure Framework - Changes to the Disclosure Requirements for Defined Benefit Plans The ASU amends ASC 715 to add, remove and clarify disclosure requirements related to defined benefit pension and other postretirement plans. Under evaluation. 2021

Basis of Presentation and Sum_3

Basis of Presentation and Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Jun. 28, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of New Accounting Pronouncements and Changes in Accounting Principles	A summary of recently adopted accounting guidance is as follows. Adoption dates are on the first day of the fiscal year indicated below, unless otherwise specified. ASU Description of ASU Impact to Atkore Note Adoption Date 2014-09 Revenue from Contracts with Customers and subsequent amendments The Accounting Standards Update ("ASU") provides guidance for revenue recognition. The update's core principle is that a company will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. In doing so, companies will need to use more judgment and make more estimates than under current guidance. Examples of the use of judgments and estimates may include identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. The update also requires more detailed disclosures to enable users of financial statements to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. The update provides for two transition methods to the new guidance: a full retrospective approach and a modified retrospective approach. The Company adopted the guidance in the first quarter of 2019 using the modified retrospective method. See Note 2, "Revenue from Contracts with Customers" for further detail. 2 2019 2018-02 Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income The ASU provided entities with the option to reclassify tax effects stranded in accumulated other comprehensive income as a result of the "H.R.1", also known as the "Tax Cuts and Jobs Act" ("TCJA") to retained earnings. The Company elected to adopt the guidance early in the quarter ended March 29, 2019. As a result of adoption of the ASU, the Company reclassified $2,333 of stranded tax benefits related to its pension plans out of Accumulated other comprehensive loss and into Accumulated deficit for the quarter ended March 29, 2019. The Company's policy is to release the tax effects as the related amounts in other comprehensive income are recognized in net income. 10 2019 2018-07 Improvements to Nonemployee Share-Based Payment Accounting. The ASU simplifies the accounting for share-based payments to nonemployees by aligning it with the accounting for share-based payments to employees, with certain exceptions. The Company elected to adopt the guidance early in the quarter ended June 28, 2019. There was no material impact to the consolidated financial statements as a result of the adoption of ASU 2018-07. 2019 2018-13 Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement The ASU amends Accounting Standard Codification ("ASC") 820 to add, remove and clarify disclosure requirements related to fair value measurements. The Company elected to adopt the guidance early in the quarter ended June 28, 2019. There was no material impact to the consolidated financial statements as a result of the adoption of ASU 2018-13. 2019 A summary of accounting guidance not yet adopted is as follows. Effective dates are on the first day of the fiscal year indicated below, unless otherwise specified. ASU Description of ASU Impact to Atkore Effective Date 2016-02 Leases (Topic 842) The ASU requires companies to use a "right of use" lease model that assumes that each lease creates an asset (the lessee's right to use the leased asset) and a liability (the future rent payment obligations), which should be reflected on a lessee's balance sheet to fairly represent the lease transaction and the lessee's related financial obligations with terms of more than 12 months. The Company will adopt the new lease guidance in the first quarter of fiscal 2020. The Company has established an implementation team, deployed lease landscape surveys, selected a software provider, completed lease data abstraction, progressed on software implementation and is currently evaluating the impact of adoption of this ASU on its consolidated financial statements. 2020 2016-13 Financial Instruments - Credit Losses (Topic 326) The ASU adds to U.S. GAAP an impairment model (known as the current expected credit loss (CECL) model) that is based on expected losses rather than incurred losses. Under the new guidance, an entity recognizes as an allowance its estimate of expected credit losses, which the FASB believes will result in more timely recognition of such losses. Under evaluation. 2021 2018-14 Disclosure Framework - Changes to the Disclosure Requirements for Defined Benefit Plans The ASU amends ASC 715 to add, remove and clarify disclosure requirements related to defined benefit pension and other postretirement plans. Under evaluation. 2021 June 28, 2019 was as follows: As of June 28, 2019 Balance Sheet As Reported Balances before adoption of ASC 606 Effect of Adoption Higher/(Lower) Accounts receivable, net 322,156 283,482 38,674 Customer liabilities 42,922 4,248 38,674

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	9 Months Ended
	Jun. 28, 2019
Revenue from Contract with Customer [Abstract]
Schedule of New Accounting Pronouncements and Changes in Accounting Principles	A summary of recently adopted accounting guidance is as follows. Adoption dates are on the first day of the fiscal year indicated below, unless otherwise specified. ASU Description of ASU Impact to Atkore Note Adoption Date 2014-09 Revenue from Contracts with Customers and subsequent amendments The Accounting Standards Update ("ASU") provides guidance for revenue recognition. The update's core principle is that a company will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. In doing so, companies will need to use more judgment and make more estimates than under current guidance. Examples of the use of judgments and estimates may include identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. The update also requires more detailed disclosures to enable users of financial statements to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. The update provides for two transition methods to the new guidance: a full retrospective approach and a modified retrospective approach. The Company adopted the guidance in the first quarter of 2019 using the modified retrospective method. See Note 2, "Revenue from Contracts with Customers" for further detail. 2 2019 2018-02 Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income The ASU provided entities with the option to reclassify tax effects stranded in accumulated other comprehensive income as a result of the "H.R.1", also known as the "Tax Cuts and Jobs Act" ("TCJA") to retained earnings. The Company elected to adopt the guidance early in the quarter ended March 29, 2019. As a result of adoption of the ASU, the Company reclassified $2,333 of stranded tax benefits related to its pension plans out of Accumulated other comprehensive loss and into Accumulated deficit for the quarter ended March 29, 2019. The Company's policy is to release the tax effects as the related amounts in other comprehensive income are recognized in net income. 10 2019 2018-07 Improvements to Nonemployee Share-Based Payment Accounting. The ASU simplifies the accounting for share-based payments to nonemployees by aligning it with the accounting for share-based payments to employees, with certain exceptions. The Company elected to adopt the guidance early in the quarter ended June 28, 2019. There was no material impact to the consolidated financial statements as a result of the adoption of ASU 2018-07. 2019 2018-13 Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement The ASU amends Accounting Standard Codification ("ASC") 820 to add, remove and clarify disclosure requirements related to fair value measurements. The Company elected to adopt the guidance early in the quarter ended June 28, 2019. There was no material impact to the consolidated financial statements as a result of the adoption of ASU 2018-13. 2019 A summary of accounting guidance not yet adopted is as follows. Effective dates are on the first day of the fiscal year indicated below, unless otherwise specified. ASU Description of ASU Impact to Atkore Effective Date 2016-02 Leases (Topic 842) The ASU requires companies to use a "right of use" lease model that assumes that each lease creates an asset (the lessee's right to use the leased asset) and a liability (the future rent payment obligations), which should be reflected on a lessee's balance sheet to fairly represent the lease transaction and the lessee's related financial obligations with terms of more than 12 months. The Company will adopt the new lease guidance in the first quarter of fiscal 2020. The Company has established an implementation team, deployed lease landscape surveys, selected a software provider, completed lease data abstraction, progressed on software implementation and is currently evaluating the impact of adoption of this ASU on its consolidated financial statements. 2020 2016-13 Financial Instruments - Credit Losses (Topic 326) The ASU adds to U.S. GAAP an impairment model (known as the current expected credit loss (CECL) model) that is based on expected losses rather than incurred losses. Under the new guidance, an entity recognizes as an allowance its estimate of expected credit losses, which the FASB believes will result in more timely recognition of such losses. Under evaluation. 2021 2018-14 Disclosure Framework - Changes to the Disclosure Requirements for Defined Benefit Plans The ASU amends ASC 715 to add, remove and clarify disclosure requirements related to defined benefit pension and other postretirement plans. Under evaluation. 2021 June 28, 2019 was as follows: As of June 28, 2019 Balance Sheet As Reported Balances before adoption of ASC 606 Effect of Adoption Higher/(Lower) Accounts receivable, net 322,156 283,482 38,674 Customer liabilities 42,922 4,248 38,674

Acquisitions (Tables)

Acquisitions (Tables)	9 Months Ended
	Jun. 28, 2019
Business Combinations [Abstract]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	The following table summarizes the Level 3 fair values assigned to the net assets acquired and liabilities assumed as of the acquisition date: (in thousands) Vergokan Fair value of consideration transferred: Cash consideration $ 58,728 Fair value of assets acquired and liabilities assumed: Cash 829 Accounts receivable 8,761 Inventories 11,434 Intangible assets 12,621 Fixed assets 32,490 Accounts payable (18,716 ) Other 1,680 Net assets acquired 49,099 Excess purchase price attributed to goodwill acquired $ 9,629
Schedule of Finite-Lived Intangible Assets Acquired as Part of Business Combination	The following table summarizes the fair value of intangible assets as of the acquisition date: Vergokan ($ in thousands) Fair Value Weighted Average Useful Life (Years) Customer relationships $ 10,535 12.0 Other 2,086 9.0 Total intangible assets $ 12,621

Divestitures (Tables)

Divestitures (Tables)	9 Months Ended
	Jun. 28, 2019
Discontinued Operations and Disposal Groups [Abstract]
Selling Price Allocation	The cash consideration received, net assets disposed and resulting gain on sale are as follows: (in thousands) FlexHead Cash consideration $ 42,631 Net assets divested 15,056 Gain on sale of a business $ 27,575

Postretirement Benefits (Tables

Postretirement Benefits (Tables)	9 Months Ended
	Jun. 28, 2019
Retirement Benefits [Abstract]
Schedule of Net Periodic Benefit Cost	The net periodic benefit credit was as follows: Three months ended Nine months ended (in thousands) Note June 28, 2019 June 29, 2018 June 28, 2019 June 29, 2018 Interest cost 1,166 1,025 $ 3,498 $ 3,074 Expected return on plan assets (1,593 ) (1,604 ) (4,779 ) (4,811 ) Amortization of actuarial loss 25 86 75 257 Net periodic benefit credit 7 $ (402 ) $ (493 ) $ (1,206 ) $ (1,480 )

Restructuring Charges (Tables)

Restructuring Charges (Tables)	9 Months Ended
	Jun. 28, 2019
Restructuring and Related Activities [Abstract]
Schedule of Restructuring Reserves	The liability for restructuring reserves is included within other current liabilities in the Company's condensed consolidated balance sheets as follows: Electrical Raceway MP&S Other/Corporate (in thousands) Severance (a) Other (a) Severance Other Severance Total Balance as of September 30, 2017 $ 449 $ — $ 278 $ 10 $ — $ 737 Charges 536 1,130 97 179 98 2,040 Utilization (787 ) (820 ) (178 ) (160 ) (98 ) (2,043 ) Reversal — — (191 ) — — (191 ) Exchange rate effects 14 — (6 ) — — 8 Balance as of September 30, 2018 212 310 — 29 — 551 Charges 681 2,500 — — — 3,181 Utilization (806 ) (2,751 ) — (29 ) — (3,586 ) Balance as of June 28, 2019 $ 87 $ 59 $ — $ — $ — $ 146 (a) Primarily related to Atkore's commitment to close certain facilities as part of its continuing effort to realign its strategic focus. The Company recorded severance restructuring charges of $681 and $327 related to termination benefits during the nine months ended June 28, 2019 and June 29, 2018 , respectively. The Company recorded other restructuring charges to close facilities of $2,473 and $600 for the nine months ended June 28, 2019 and June 29, 2018 , respectively.
Restructuring and Related Costs	The net restructuring charges included as a component of selling, general and administrative expenses in the Company's condensed consolidated statements of operations were as follows: Three months ended Nine months ended (in thousands) June 28, 2019 June 29, 2018 June 28, 2019 June 29, 2018 Total restructuring charges, net $ 709 $ 407 $ 3,181 $ 1,245

Other (Income) Expense, Net (Ta

Other (Income) Expense, Net (Tables)	9 Months Ended
	Jun. 28, 2019
Other Income and Expenses [Abstract]
Schedule of Other Expense, Net	Other (income) expense, net consisted of the following: Three months ended Nine months ended (in thousands) June 28, 2019 June 29, 2018 June 28, 2019 June 29, 2018 Gain on sale of a business — (838 ) — (27,575 ) Undesignated foreign currency derivative instruments (2,095 ) (3,757 ) (3,562 ) (22 ) Foreign exchange (gain) loss on intercompany loans 1,360 3,374 1,423 795 Debt modification costs — — — 892 Pension-related benefits (402 ) (493 ) (1,206 ) (1,480 ) Other (91 ) (126 ) (77 ) (126 ) Other (income) expense, net $ (1,228 ) $ (1,840 ) $ (3,422 ) $ (27,516 )

Earnings Per Share (Tables)

Earnings Per Share (Tables)	9 Months Ended
	Jun. 28, 2019
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Net Income Per Share	The following table sets forth the computation of basic and diluted earnings per share: Three months ended Nine months ended (in thousands, except per share data) June 28, 2019 June 29, 2018 June 28, 2019 June 29, 2018 Numerator: Net income $ 36,550 $ 34,199 $ 93,054 $ 103,946 Less: Undistributed earnings allocated to participating securities 996 422 2,499 1,048 Net income available to common shareholders $ 35,554 $ 33,777 $ 90,555 $ 102,898 Denominator: Basic weighted average common shares outstanding 46,386 46,262 46,481 53,592 Effect of dilutive securities: Non-participating employee stock options (1) 1,171 2,150 1,254 2,423 Diluted weighted average common shares outstanding 47,557 48,412 47,735 56,015 Basic earnings per share $ 0.77 $ 0.73 $ 1.95 $ 1.92 Diluted earnings per share $ 0.75 $ 0.70 $ 1.90 $ 1.84 (1) Stock options to purchase approximately 0.3 million and 0.4 million shares of common stock were outstanding during the three months ended June 28, 2019 and June 29, 2018, respectively, but were not included in the calculation of diluted earnings per share as the impact of these options would have been anti-dilutive. Stock options to purchase approximately 0.4 million and 0.4 million shares of common stock were outstanding during the nine months ended June 28, 2019 and June 29, 2018, respectively, but were not included in the calculation of diluted earnings per share as the impact of these options would have been anti-dilutive.

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Loss (Tables)	9 Months Ended
	Jun. 28, 2019
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Loss	The following table presents the changes in accumulated other comprehensive loss by component for the nine months ended June 28, 2019 and June 29, 2018 : (in thousands) Defined benefit pension items Currency translation adjustments Total Balance as of September 30, 2018 $ (6,048 ) $ (10,390 ) $ (16,438 ) Other comprehensive loss before reclassifications — (2,404 ) (2,404 ) Amounts reclassified from accumulated other 60 — 60 Net current period other comprehensive income (loss) 60 (2,404 ) (2,344 ) Reclassification of stranded tax benefits (1) (2,333 ) — (2,333 ) Balance as of June 28, 2019 $ (8,321 ) $ (12,794 ) $ (21,115 ) (1) Due to the adoption of ASU 2018-02. (in thousands) Defined benefit pension items Currency translation adjustments Total Balance as of September 30, 2017 $ (10,445 ) $ (7,537 ) $ (17,982 ) Other comprehensive income before reclassifications — (1,793 ) (1,793 ) Amounts reclassified from accumulated other 194 — 194 Net current period other comprehensive income (loss) 194 (1,793 ) (1,599 ) Balance as of June 29, 2018 $ (10,251 ) $ (9,330 ) $ (19,581 ) The following table presents the changes in accumulated other comprehensive loss by component for the three months ended June 28, 2019 and June 29, 2018 : (in thousands) Defined benefit pension items Currency translation adjustments Total Balance as of March 29, 2019 $ (8,341 ) $ (12,184 ) $ (20,525 ) Other comprehensive income before reclassifications — (610 ) (610 ) Amounts reclassified from accumulated other 20 — 20 Net current period other comprehensive income (loss) 20 (610 ) (590 ) Balance as of June 28, 2019 $ (8,321 ) $ (12,794 ) $ (21,115 ) (in thousands) Defined benefit pension items Currency translation adjustments Total Balance as of March 30 2018 $ (10,316 ) $ (6,037 ) $ (16,353 ) Other comprehensive income before reclassifications — (3,293 ) (3,293 ) Amounts reclassified from accumulated other 65 — 65 Net current period other comprehensive income (loss) 65 (3,293 ) (3,228 ) Balance as of June 29, 2018 $ (10,251 ) $ (9,330 ) $ (19,581 )

Inventories, Net (Tables)

Inventories, Net (Tables)	9 Months Ended
	Jun. 28, 2019
Inventory Disclosure [Abstract]
Schedule of Inventory, Current	Interim LIFO determinations, including those at June 28, 2019 , are based on management's estimates of future inventory levels and costs for the remainder of the current fiscal year. (in thousands) June 28, 2019 September 30, 2018 Purchased materials and manufactured parts, net $ 48,742 $ 58,572 Work in process, net 24,730 21,769 Finished goods, net 151,299 141,412 Inventories, net $ 224,771 $ 221,753

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	9 Months Ended
	Jun. 28, 2019
Property, Plant and Equipment [Abstract]
Schedule of Property, Plant and Equipment	As of June 28, 2019 , and September 30, 2018 , property, plant and equipment at cost and accumulated depreciation were as follows: (in thousands) June 28, 2019 September 30, 2018 Land $ 19,901 $ 13,295 Buildings and related improvements 122,452 108,758 Machinery and equipment 295,878 262,078 Leasehold improvements 8,347 7,382 Software 24,367 30,502 Construction in progress 17,826 16,777 Property, plant and equipment 488,771 438,792 Accumulated depreciation (251,206 ) (225,684 ) Property, plant and equipment, net $ 237,565 $ 213,108

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	9 Months Ended
	Jun. 28, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	Changes in the carrying amount of goodwill are as follows: (in thousands) Electrical Raceway Mechanical Products & Solutions Total Balance as of October 1, 2018 $ 133,566 $ 36,563 $ 170,129 Goodwill acquired during year 19,766 — 19,766 Exchange rate effects (845 ) — (845 ) Balance as of June 28, 2019 $ 152,487 $ 36,563 $ 189,050
Schedule of Finite-Lived Intangible Assets	The following table provides the gross carrying value, accumulated amortization and net carrying value for each major class of intangible assets: June 28, 2019 September 30, 2018 ($ in thousands) Weighted Average Useful Life (Years) Gross Carrying Value Accumulated Amortization Net Carrying Value Gross Carrying Value Accumulated Amortization Net Carrying Value Amortizable intangible assets: Customer relationships 11 $ 351,597 $ (164,099 ) $ 187,498 $ 330,295 $ (141,401 ) $ 188,894 Other 8 18,086 (7,276 ) 10,810 16,003 (5,861 ) 10,142 Total 369,683 (171,375 ) 198,308 346,298 (147,262 ) 199,036 Indefinite-lived intangible assets: Trade names 92,880 — 92,880 92,880 — 92,880 Total $ 462,563 $ (171,375 ) $ 291,188 $ 439,178 $ (147,262 ) $ 291,916
Schedule of Indefinite-Lived Intangible Assets	The following table provides the gross carrying value, accumulated amortization and net carrying value for each major class of intangible assets: June 28, 2019 September 30, 2018 ($ in thousands) Weighted Average Useful Life (Years) Gross Carrying Value Accumulated Amortization Net Carrying Value Gross Carrying Value Accumulated Amortization Net Carrying Value Amortizable intangible assets: Customer relationships 11 $ 351,597 $ (164,099 ) $ 187,498 $ 330,295 $ (141,401 ) $ 188,894 Other 8 18,086 (7,276 ) 10,810 16,003 (5,861 ) 10,142 Total 369,683 (171,375 ) 198,308 346,298 (147,262 ) 199,036 Indefinite-lived intangible assets: Trade names 92,880 — 92,880 92,880 — 92,880 Total $ 462,563 $ (171,375 ) $ 291,188 $ 439,178 $ (147,262 ) $ 291,916
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense	Expected amortization expense for intangible assets for the remainder of fiscal 2019 and over the next five years and thereafter is as follows: (in thousands) Remaining 2019 $ 9,888 2020 31,581 2021 31,447 2022 30,113 2023 29,993 2024 25,614 Thereafter 39,672

Debt (Tables)

Debt (Tables)	9 Months Ended
	Jun. 28, 2019
Debt Disclosure [Abstract]
Schedule of Debt	Debt as of June 28, 2019 and September 30, 2018 was as follows: (in thousands) June 28, 2019 September 30, 2018 First Lien Term Loan Facility due December 22, 2023 $ 891,317 $ 912,162 Deferred financing costs (6,976 ) (8,194 ) Other 162 279 Total debt $ 884,503 $ 904,247 Less: Current portion — 26,561 Long-term debt $ 884,503 $ 877,686

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Jun. 28, 2019
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities	The following table presents the Company's assets and liabilities measured at fair value: June 28, 2019 September 30, 2018 (in thousands) Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 Assets Cash equivalents $ 57,089 $ — $ — $ 28,175 $ — $ — Forward currency contracts — 1,686 — — — — Liabilities Forward currency contracts — 87 — — 1,857 —
Estimated Fair Value of Financial Instruments Not Carried at Fair Value	The estimated fair value of financial instruments not carried at fair value in the condensed consolidated balance sheets were as follows: June 28, 2019 September 30, 2018 (in thousands) Carrying Value Fair Value Carrying Value Fair Value First Lien Term Loan Facility due December 22, 2023 $ 892,120 $ 888,195 $ 913,100 $ 916,113

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Jun. 28, 2019
Segment Reporting [Abstract]
Schedule of Segment Information	Presented below is a reconciliation of operating segment Adjusted EBITDA to Income before income taxes : Three months ended Nine months ended (in thousands) June 28, 2019 June 29, 2018 June 28, 2019 June 29, 2018 Operating segment Adjusted EBITDA Electrical Raceway $ 76,721 $ 74,461 $ 212,585 $ 187,025 MP&S 20,595 12,013 48,903 39,544 Total 97,316 86,474 261,488 226,569 Unallocated expenses (a) (8,835 ) (9,810 ) (25,890 ) (26,077 ) Depreciation and amortization (17,760 ) (16,192 ) (54,061 ) (49,255 ) Interest expense, net (12,789 ) (12,442 ) (38,277 ) (28,322 ) Restructuring and impairments (709 ) (407 ) (3,181 ) (1,245 ) Stock-based compensation (4,120 ) (3,494 ) (8,936 ) (9,828 ) Certain legal matters — — — (2,286 ) Transaction costs (76 ) (768 ) (363 ) (2,676 ) Gain on sale of a business — 838 — 27,575 Other (b) (5,371 ) 352 (8,213 ) (2,249 ) Income before income taxes $ 47,656 $ 44,551 $ 122,567 $ 132,206 (a) Represents unallocated selling, general and administrative activities and associated expenses including, in part, executive, legal, finance, human resources, information technology, business development and communications, as well as certain costs and earnings of employee-related benefits plans, such as stock-based compensation and a portion of self-insured medical costs. (b) Represents other items, such as inventory reserves and adjustments, release of indemnified uncertain tax positions and the impact of foreign exchange gains or losses. Three months ended June 28, 2019 June 29, 2018 (in thousands) External Net Sales Intersegment Sales Adjusted EBITDA External Net Sales Intersegment Sales Adjusted EBITDA Electrical Raceway $ 372,895 $ 334 $ 76,721 $ 369,812 $ 521 $ 74,461 MP&S 120,596 — 20,595 128,202 37 12,013 Eliminations — (334 ) — (558 ) Consolidated operations $ 493,491 $ — $ 498,014 $ — Nine months ended June 28, 2019 June 29, 2018 (in thousands) External Net Sales Intersegment Sales Adjusted EBITDA External Net Sales Intersegment Sales Adjusted EBITDA Electrical Raceway $ 1,069,229 $ 920 $ 212,585 $ 1,010,523 $ 1,120 $ 187,025 MP&S 345,599 — 48,903 347,049 74 39,544 Eliminations — (920 ) — (1,194 ) Consolidated operations $ 1,414,828 $ — $ 1,357,572 $ —
Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas	The Company's net sales by geography were as follows for the three and nine months ended June 28, 2019 and June 29, 2018 : Three months ended Nine months ended (in thousands) June 28, 2019 June 29, 2018 June 28, 2019 June 29, 2018 United States $ 436,767 $ 449,907 $ 1,240,402 $ 1,222,573 Other Americas 7,821 11,938 26,030 29,653 Europe 36,277 23,822 108,947 67,507 Asia-Pacific 12,626 12,347 39,449 37,839 Total $ 493,491 $ 498,014 $ 1,414,828 $ 1,357,572 The table below shows the amount of net sales from external customers for each of the Company's product categories which accounted for 10% or more of consolidated net sales in either period for the three and nine months ended June 28, 2019 and June 29, 2018 : Three months ended Nine months ended (in thousands) June 28, 2019 June 29, 2018 June 28, 2019 June 29, 2018 Metal Electrical Conduit and Fittings $ 139,342 $ 146,497 $ 404,720 375,507 Armored Cable and Fittings 90,891 84,686 263,864 253,727 PVC Electrical Conduit and Fittings 78,765 86,742 213,181 234,101 Cable Tray and Cable Ladders 50,680 37,715 147,592 108,814 Other raceway products 13,217 14,172 39,872 38,374 Electrical Raceway 372,895 369,812 1,069,229 1,010,523 Mechanical Pipe 63,502 71,756 186,209 182,268 Metal Framing and Fittings 29,328 31,234 88,389 83,544 Other MP&S products 27,766 25,212 71,001 71,854 Impact of Fence and Sprinkler — — — 9,383 MP&S 120,596 128,202 345,599 347,049 Net sales $ 493,491 $ 498,014 $ 1,414,828 $ 1,357,572

Basis of Presentation and Sum_4

Basis of Presentation and Summary of Significant Accounting Policies Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 28, 2019	Mar. 29, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of Stranded Tax Benefits		$ 0
Accumulated Deficit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of Stranded Tax Benefits	$ 2,333	$ 2,333

Revenue from Contracts with C_3

Revenue from Contracts with Customers (Details) - USD ($) $ in Thousands	Jun. 28, 2019	Sep. 30, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts Receivable, net	$ 322,156	$ 265,147
Customer liabilities	42,922	$ 3,377
Balances before adoption of ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts Receivable, net	283,482
Customer liabilities	4,248
Effect of Adoption Higher/(Lower)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts Receivable, net	38,674
Customer liabilities	$ 38,674

Acquisitions - Narrative (Detai

Acquisitions - Narrative (Details) - USD ($) $ in Thousands	Jun. 03, 2019	Oct. 01, 2018	Jan. 08, 2018	Jun. 28, 2019	Jun. 29, 2018	Sep. 30, 2018
Business Acquisition [Line Items]
Acquisition of businesses, net of cash acquired				$ 83,385	$ 3,350
Goodwill				189,050		$ 170,129
United Structural Products, LLC.
Business Acquisition [Line Items]
Acquisition of businesses, net of cash acquired	$ 25,486
Goodwill	10,137
Identifiable Intangible Assets	11,937
Working capital and other tangible assets	$ 3,412
Communications Integrators, Inc.
Business Acquisition [Line Items]
Purchase price			$ 3,997
Selling, General and Administrative Expenses | Vergokan
Business Acquisition [Line Items]
Acquisition of businesses, net of cash acquired		$ 57,899
Acquisition related expenses				$ 148		$ 293

Acquisitions - Summary of Level

Acquisitions - Summary of Level 3 Fair Values Assigned to Net Assets Acquired and Liabilities Assumed As of Acquisition Date (Details) - Vergokan $ in Thousands	Oct. 01, 2018USD ($)
Fair value of consideration transferred:
Cash consideration	$ 58,728
Fair value of assets acquired and liabilities assumed:
Cash	829
Accounts receivable	8,761
Inventories	11,434
Intangible assets	12,621
Fixed assets	32,490
Accounts payable	(18,716)
Other	1,680
Net assets acquired	49,099
Electrical Raceway
Fair value of assets acquired and liabilities assumed:
Excess purchase price attributed to goodwill acquired	$ 9,629

Acquisitions - Summary of Fair

Acquisitions - Summary of Fair Value as of Acquisition Date (Details) - Vergokan $ in Thousands	Oct. 01, 2018USD ($)
Business Acquisition [Line Items]
Fair Value	$ 12,621
Weighted Average Useful Life (Years)
Customer relationships
Business Acquisition [Line Items]
Fair Value	$ 10,535
Weighted Average Useful Life (Years)	12 years
Other
Business Acquisition [Line Items]
Fair Value	$ 2,086
Weighted Average Useful Life (Years)	9 years

Divestitures (Details)

Divestitures (Details) - USD ($) $ in Thousands	Mar. 30, 2018	Jun. 29, 2018	Jun. 28, 2019	Jun. 29, 2018	Sep. 30, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash consideration			$ 0	$ 42,631
Goodwill			$ 189,050		$ 170,129
Gain on sale of business, working capital adjustment		$ (838)		$ 838
Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Goodwill	$ 2,626
FlexHead Industries, Inc and SprinkFLEX, LLC | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash consideration	42,631
Net assets divested	15,056
Gain on sale of a business	$ 27,575

Postretirement Benefits - Net P

Postretirement Benefits - Net Periodic Benefit Cost (Details) - Pension Plan - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 28, 2019	Jun. 29, 2018	Jun. 28, 2019	Jun. 29, 2018
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 1,166	$ 1,025	$ 3,498	$ 3,074
Expected return on plan assets	(1,593)	(1,604)	(4,779)	(4,811)
Amortization of actuarial loss	25	86	75	257
Net periodic benefit credit	$ (402)	$ (493)	$ (1,206)	$ (1,480)

Restructuring Charges - Restruc

Restructuring Charges - Restructuring Reserves (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Jun. 28, 2019	Jun. 29, 2018	Sep. 30, 2018
Restructuring Reserve [Roll Forward]
Beginning balance	$ 551	$ 737	$ 737
Charges	3,181		2,040
Utilization	(3,586)		(2,043)
Reversals/exchange rate effects			(191)
Exchange rate effects			8
Ending balance	146		551
One-time Termination Benefits
Restructuring Reserve [Roll Forward]
Charges	681	327
Facility Closing
Restructuring Reserve [Roll Forward]
Charges	2,473	600
Operating Segments | Electrical Raceway | Severance
Restructuring Reserve [Roll Forward]
Beginning balance	212	449	449
Charges	681		536
Utilization	(806)		(787)
Reversals/exchange rate effects			0
Exchange rate effects			14
Ending balance	87		212
Operating Segments | Electrical Raceway | Other
Restructuring Reserve [Roll Forward]
Beginning balance	310	0	0
Charges	2,500		1,130
Utilization	(2,751)		(820)
Reversals/exchange rate effects			0
Exchange rate effects			0
Ending balance	59		310
Operating Segments | MP&S | Severance
Restructuring Reserve [Roll Forward]
Beginning balance	0	278	278
Charges	0		97
Utilization	0		(178)
Reversals/exchange rate effects			(191)
Exchange rate effects			(6)
Ending balance	0		0
Operating Segments | MP&S | Other
Restructuring Reserve [Roll Forward]
Beginning balance	29	10	10
Charges	0		179
Utilization	(29)		(160)
Reversals/exchange rate effects			0
Exchange rate effects			0
Ending balance	0		29
Corporate, Non-Segment | Severance
Restructuring Reserve [Roll Forward]
Beginning balance	0	$ 0	0
Charges	0		98
Utilization	0		(98)
Reversals/exchange rate effects			0
Exchange rate effects			0
Ending balance	$ 0		$ 0

Restructuring Charges - As a Co

Restructuring Charges - As a Component of Selling, General and Administrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 28, 2019	Jun. 29, 2018	Jun. 28, 2019	Jun. 29, 2018
Restructuring and Related Activities [Abstract]
Total restructuring charges, net	$ 709	$ 407	$ 3,181	$ 1,245

Other (Income) Expense, Net (De

Other (Income) Expense, Net (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 28, 2019	Jun. 29, 2018	Jun. 28, 2019	Jun. 29, 2018
Other Income and Expenses [Abstract]
Gain on sale of a business	$ 0	$ (838)	$ 0	$ (27,575)
Undesignated foreign currency derivative instruments	(2,095)	(3,757)	(3,562)	(22)
Foreign exchange (gain) loss on intercompany loans	1,360	3,374	1,423	795
Debt modification costs	0	0	0	892
Pension-related benefits	(402)	(493)	(1,206)	(1,480)
Other	(91)	(126)	(77)	(126)
Other (income) expense, net	$ (1,228)	$ (1,840)	$ (3,422)	$ (27,516)

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	Dec. 22, 2017	Dec. 21, 2017	Jun. 28, 2019	Jun. 29, 2018	Dec. 29, 2017	Jun. 28, 2019	Jun. 29, 2018	Sep. 30, 2018
Operating Loss Carryforwards [Line Items]
Federal corporate tax rate	21.00%	35.00%
Effective income tax rate reconciliation, effect of Tax Cuts and Jobs Act of 2017, amount					$ 4,758			$ 708
Effective income tax rate			23.30%	23.20%		24.10%	21.40%
Income tax expense			$ 11,106	$ 10,352		$ 29,513	$ 28,260
Decrease unrecognized tax benefits			13			549
Other Deferred Tax Assets
Operating Loss Carryforwards [Line Items]
Valuation allowance, deferred tax asset, amount			$ 284			$ 550

Earnings Per Share (Details)

Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Jun. 28, 2019	Mar. 29, 2019	Dec. 28, 2018	Jun. 29, 2018	Mar. 30, 2018	Dec. 29, 2017	Jun. 28, 2019	Jun. 29, 2018
Numerator:
Net income	$ 36,550	$ 29,555	$ 26,949	$ 34,199	$ 42,558	$ 27,189	$ 93,054	$ 103,946
Less: Undistributed earnings allocated to participating securities	996			422			2,499	1,048
Net income available to common shareholders	$ 35,554			$ 33,777			$ 90,555	$ 102,898
Denominator:
Weighted-average shares outstanding - Basic (in shares)	46,386			46,262			46,481	53,592
Effect of dilutive securities: Non-participating employee stock options (in shares)	1,171			2,150			1,254	2,423
Weighted-average shares outstanding - diluted (in shares)	47,557			48,412			47,735	56,015
Basic earnings per share (in dollars per share)	$ 0.77			$ 0.73			$ 1.95	$ 1.92
Diluted earnings per share (in dollars per share)	$ 0.75			$ 0.70			$ 1.90	$ 1.84

Earnings Per Share - Antidiluti

Earnings Per Share - Antidilutive Securities (Details) - shares shares in Millions	3 Months Ended		9 Months Ended
	Jun. 28, 2019	Jun. 29, 2018	Jun. 28, 2019	Jun. 29, 2018
Common Stock | Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from calculation of diluted earnings per share (in shares)	0.3	0.4	0.4	0.4

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Loss - Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Jun. 28, 2019	Mar. 29, 2019	Dec. 28, 2018	Jun. 29, 2018	Mar. 30, 2018	Dec. 29, 2017	Jun. 28, 2019	Jun. 29, 2018
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	$ 158,497	$ 124,155	$ 122,059	$ 62,075	$ 388,668	$ 360,871	$ 122,059	$ 360,871
Other comprehensive loss before reclassifications	(610)			(3,293)			(2,404)	(1,793)
Amounts reclassified from accumulated other comprehensive loss	20			65			60	194
Total other comprehensive (loss)	(590)	967	(2,721)	(3,228)	1,233	396	(2,344)	(1,599)
Reclassification from AOCI, Current Period, Tax							(2,333)
Balance at end of period	202,518	158,497	124,155	73,763	62,075	388,668	202,518	73,763
Defined benefit pension items
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(8,341)		(6,048)	(10,316)		(10,445)	(6,048)	(10,445)
Other comprehensive loss before reclassifications	0			0			0	0
Amounts reclassified from accumulated other comprehensive loss	20			65			60	194
Total other comprehensive (loss)	20			65			60	194
Reclassification from AOCI, Current Period, Tax							(2,333)
Balance at end of period	(8,321)	(8,341)		(10,251)	(10,316)		(8,321)	(10,251)
Currency translation adjustments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(12,184)		(10,390)	(6,037)		(7,537)	(10,390)	(7,537)
Other comprehensive loss before reclassifications	(610)			(3,293)			(2,404)	(1,793)
Amounts reclassified from accumulated other comprehensive loss	0			0			0	0
Total other comprehensive (loss)	(610)			(3,293)			(2,404)	(1,793)
Reclassification from AOCI, Current Period, Tax							0
Balance at end of period	(12,794)	(12,184)		(9,330)	(6,037)		(12,794)	(9,330)
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(20,525)	(19,159)	(16,438)	(16,353)	(17,586)	(17,982)	(16,438)	(17,982)
Total other comprehensive (loss)	(590)	967	(2,721)	(3,228)	1,233	396
Balance at end of period	$ (21,115)	$ (20,525)	$ (19,159)	$ (19,581)	$ (16,353)	$ (17,586)	$ (21,115)	$ (19,581)

Inventories, Net - Narrative (D

Inventories, Net - Narrative (Details) - USD ($) $ in Thousands	Jun. 28, 2019	Sep. 30, 2018
Inventory Disclosure [Abstract]
Inventories at lower of LIFO cost or market	75.00%	80.00%
FIFO inventory amount	$ 15,888	$ 26,340
Excess and obsolete inventory reserve	$ 17,099	$ 12,909

Inventories, Net - Schedule of

Inventories, Net - Schedule of Inventory (Details) - USD ($) $ in Thousands	Jun. 28, 2019	Sep. 30, 2018
Inventory Disclosure [Abstract]
Purchased materials and manufactured parts, net	$ 48,742	$ 58,572
Work in process, net	24,730	21,769
Finished goods, net	151,299	141,412
Inventories, net	$ 224,771	$ 221,753

Property, Plant and Equipment_2

Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Jun. 28, 2019	Sep. 30, 2018
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 488,771	$ 438,792
Accumulated depreciation	(251,206)	(225,684)
Property, plant and equipment, net	237,565	213,108
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment	19,901	13,295
Buildings and related improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment	122,452	108,758
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment	295,878	262,078
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment	8,347	7,382
Software
Property, Plant and Equipment [Line Items]
Property, plant and equipment	24,367	30,502
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 17,826	$ 16,777

Property, Plant and Equipment -

Property, Plant and Equipment - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 28, 2019	Jun. 29, 2018	Jun. 28, 2019	Jun. 29, 2018
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 9,892	$ 8,498	$ 29,783	$ 25,109

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets - Change in Carrying Amount (Details) $ in Thousands	9 Months Ended
	Jun. 28, 2019USD ($)
Goodwill [Roll Forward]
Balance at beginning of period	$ 170,129
Goodwill acquired during year	19,766
Exchange rate effects	(845)
Balance at end of period	189,050
Electrical Raceway
Goodwill [Roll Forward]
Balance at beginning of period	133,566
Goodwill acquired during year	19,766
Exchange rate effects	(845)
Balance at end of period	152,487
MP&S
Goodwill [Roll Forward]
Balance at beginning of period	36,563
Goodwill acquired during year	0
Exchange rate effects	0
Balance at end of period	$ 36,563

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 28, 2019	Jun. 29, 2018	Jun. 28, 2019	Jun. 29, 2018	Oct. 01, 2018
Goodwill [Line Items]
Intangible asset amortization	$ 7,868	$ 7,694	$ 24,278	$ 24,146
Electrical Raceway
Goodwill [Line Items]
Accumulated impairment loss					$ 3,924
MP&S
Goodwill [Line Items]
Accumulated impairment loss	$ 43,000		$ 43,000

Goodwill and Intangible Asset_4

Goodwill and Intangible Assets - Intangible Assets (Details) - USD ($) $ in Thousands	9 Months Ended
	Jun. 28, 2019	Sep. 30, 2018
Amortizable intangible assets:
Gross Carrying Value	$ 369,683	$ 346,298
Accumulated Amortization	(171,375)	(147,262)
Net Carrying Value	198,308	199,036
Intangible Assets, Net (Excluding Goodwill) [Abstract]
Gross Carrying Value	462,563	439,178
Net Carrying Value	291,188	291,916
Trade names
Indefinite-lived Intangible Assets [Line Items]
Gross carrying value/net carrying value	92,880	92,880
Customer relationships
Amortizable intangible assets:
Gross Carrying Value	351,597	330,295
Accumulated Amortization	(164,099)	(141,401)
Net Carrying Value	$ 187,498	188,894
Customer relationships | Weighted Average Useful Life (Years)
Amortizable intangible assets:
Weighted Average Useful Life (Years)	11 years
Other
Amortizable intangible assets:
Gross Carrying Value	$ 18,086	16,003
Accumulated Amortization	(7,276)	(5,861)
Net Carrying Value	$ 10,810	$ 10,142
Other | Weighted Average Useful Life (Years)
Amortizable intangible assets:
Weighted Average Useful Life (Years)	8 years

Goodwill and Intangible Asset_5

Goodwill and Intangible Assets - Future Amortization Expense (Details) (Details) $ in Thousands	Jun. 28, 2019USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
Remaining 2019	$ 9,888
2020	31,581
2021	31,447
2022	30,113
2023	29,993
2024	25,614
Thereafter	$ 39,672

Debt - Schedule of Debt (Detail

Debt - Schedule of Debt (Details) - USD ($) $ in Thousands	Jun. 28, 2019	Sep. 30, 2018
Debt Instrument [Line Items]
Deferred financing costs	$ (6,976)	$ (8,194)
Other	162	279
Total debt	884,503	904,247
Less: Current portion	0	26,561
Long-term debt	884,503	877,686
Secured Debt | First Lien Term Loan Facility due December 22, 2023
Debt Instrument [Line Items]
First Lien Term Loan Facility due December 22, 2023	$ 891,317	$ 912,162

Debt - ABL Credit Facility - Na

Debt - ABL Credit Facility - Narrative (Details) - Atkore International - Line of credit - ABL Credit Facility - USD ($)	3 Months Ended
	Jun. 28, 2019	Sep. 30, 2018
Debt Instrument [Line Items]
Aggregate commitments	$ 325,000,000
Credit availability	312,550,000	$ 315,119,000
Repayments of credit facility	$ 18,680,000

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details) $ in Thousands, £ in Millions	9 Months Ended
	Jun. 28, 2019GBP (£)	Jun. 28, 2019USD ($)	Sep. 30, 2018GBP (£)	Sep. 30, 2018USD ($)
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Forward currency contracts | £	£ 45		£ 49.1
Measurement Input, Expected Term | Minimum | Foreign Exchange Contract
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Credit derivative, term	6 months
Measurement Input, Expected Term | Maximum | Foreign Exchange Contract
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Credit derivative, term	6 years
Level 3 | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Forward currency contracts | $		$ 0		$ 0

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities Measures On a Gross Basis (Details) - Fair Value, Measurements, Recurring $ in Thousands, £ in Millions	Jun. 28, 2019GBP (£)	Jun. 28, 2019USD ($)	Sep. 30, 2018GBP (£)	Sep. 30, 2018USD ($)
Assets
Forward currency contracts | £	£ 45		£ 49.1
Level 1
Assets
Cash equivalents		$ 57,089		$ 28,175
Forward currency contracts		0		0
Liabilities
Forward currency contracts		0		0
Level 2
Assets
Cash equivalents		0		0
Forward currency contracts		1,686		0
Liabilities
Forward currency contracts		87		1,857
Level 3
Assets
Cash equivalents		0		0
Forward currency contracts		0		0
Liabilities
Forward currency contracts		$ 0		$ 0

Fair Value Measurements - Estim

Fair Value Measurements - Estimated Fair Value (Details) - Secured Debt - First Lien Term Loan Facility due December 22, 2023 - USD ($) $ in Thousands	Jun. 28, 2019	Sep. 30, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	$ 892,120	$ 913,100
Fair Value	$ 888,195	$ 916,113

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) - USD ($)	Jun. 28, 2019	Sep. 30, 2018
Loss Contingencies [Line Items]
Purchase obligations for rest of fiscal year	$ 129,758,000
Purchase obligations for year two	3,317,000
Total settlement for prior cap agreement deductible	13,000,000
Special Products Claims and Other Product Liabilities | Minimum
Loss Contingencies [Line Items]
Probable losses	1,000,000
Special Products Claims and Other Product Liabilities | Maximum
Loss Contingencies [Line Items]
Probable losses	8,000,000
Special Products Claims
Loss Contingencies [Line Items]
Total settlement for cap agreement deductible	12,000,000
Other Product Liability
Loss Contingencies [Line Items]
Product liability	$ 1,204,000	$ 6,755,000

Guarantees - Narrative (Details

Guarantees - Narrative (Details) $ in Thousands	Jun. 28, 2019USD ($)
Supporting workers compensation
Guarantor Obligations [Line Items]
Guarantees	$ 10,501
Surety bond
Guarantor Obligations [Line Items]
Guarantees	$ 21,408

Segment Information - Narrative

Segment Information - Narrative (Details)	9 Months Ended
	Jun. 28, 2019segment
Segment Reporting [Abstract]
Number of operating segments	2

Segment Information - Shared As

Segment Information - Shared Assets (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 28, 2019	Jun. 29, 2018	Jun. 28, 2019	Jun. 29, 2018
Segment Reporting Information [Line Items]
Net sales	$ 493,491	$ 498,014	$ 1,414,828	$ 1,357,572
Operating segment Adjusted EBITDA	97,316	86,474	261,488	226,569
Electrical Raceway
Segment Reporting Information [Line Items]
Net sales	372,895	369,812	1,069,229	1,010,523
MP&S
Segment Reporting Information [Line Items]
Net sales	120,596	128,202	345,599	347,049
Intersegment Sales
Segment Reporting Information [Line Items]
Net sales	(334)	(558)	(920)	(1,194)
Intersegment Sales | Electrical Raceway
Segment Reporting Information [Line Items]
Net sales	334	521	920	1,120
Intersegment Sales | MP&S
Segment Reporting Information [Line Items]
Net sales	0	37	0	74
Operating Segments | Electrical Raceway
Segment Reporting Information [Line Items]
Operating segment Adjusted EBITDA	76,721	74,461	212,585	187,025
Operating Segments | MP&S
Segment Reporting Information [Line Items]
Operating segment Adjusted EBITDA	$ 20,595	$ 12,013	$ 48,903	$ 39,544

Segment Information - Reconcili

Segment Information - Reconciliation of Operating Segment Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 28, 2019	Jun. 29, 2018	Jun. 28, 2019	Jun. 29, 2018
Segment Reporting Information [Line Items]
Operating segment Adjusted EBITDA	$ 97,316	$ 86,474	$ 261,488	$ 226,569
Unallocated expenses	(8,835)	(9,810)	(25,890)	(26,077)
Depreciation and amortization	(17,760)	(16,192)	(54,061)	(49,255)
Interest expense, net	(12,789)	(12,442)	(38,277)	(28,322)
Restructuring and impairments	(709)	(407)	(3,181)	(1,245)
Stock-based compensation	(4,120)	(3,494)	(8,936)	(9,828)
Certain legal matters	0	0	0	(2,286)
Transaction costs	(76)	(768)	(363)	(2,676)
Gain on sale of a business	0	838	0	27,575
Other	(5,371)	352	(8,213)	(2,249)
Income before income taxes	47,656	44,551	122,567	132,206
Operating Segments | Electrical Raceway
Segment Reporting Information [Line Items]
Operating segment Adjusted EBITDA	76,721	74,461	212,585	187,025
Operating Segments | MP&S
Segment Reporting Information [Line Items]
Operating segment Adjusted EBITDA	$ 20,595	$ 12,013	$ 48,903	$ 39,544

Segment Information - Net Sales

Segment Information - Net Sales by Geography (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 28, 2019	Jun. 29, 2018	Jun. 28, 2019	Jun. 29, 2018
Disaggregation of Revenue [Line Items]
Net sales	$ 493,491	$ 498,014	$ 1,414,828	$ 1,357,572
United States
Disaggregation of Revenue [Line Items]
Net sales	436,767	449,907	1,240,402	1,222,573
Other Americas
Disaggregation of Revenue [Line Items]
Net sales	7,821	11,938	26,030	29,653
Europe
Disaggregation of Revenue [Line Items]
Net sales	36,277	23,822	108,947	67,507
Asia-Pacific
Disaggregation of Revenue [Line Items]
Net sales	$ 12,626	$ 12,347	$ 39,449	$ 37,839

Segment Information - Net Sal_2

Segment Information - Net Sales (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 28, 2019	Jun. 29, 2018	Jun. 28, 2019	Jun. 29, 2018
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	$ 493,491	$ 498,014	$ 1,414,828	$ 1,357,572
Electrical Raceway
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	372,895	369,812	1,069,229	1,010,523
MP&S
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	120,596	128,202	345,599	347,049
Metal Electrical Conduit and Fittings | Electrical Raceway
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	139,342	146,497	404,720	375,507
Armored Cable and Fittings | Electrical Raceway
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	90,891	84,686	263,864	253,727
PVC Electrical Conduit and Fittings | Electrical Raceway
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	78,765	86,742	213,181	234,101
Cable Tray and Cable Ladders | Electrical Raceway
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	50,680	37,715	147,592	108,814
Other raceway products | Electrical Raceway
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	13,217	14,172	39,872	38,374
Mechanical Pipe | MP&S
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	63,502	71,756	186,209	182,268
Metal Framing and Fittings | MP&S
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	29,328	31,234	88,389	83,544
Other MP&S products | MP&S
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	27,766	25,212	71,001	71,854
Impact of Fence and Sprinkler | MP&S
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	$ 0	$ 0	$ 0	$ 9,383