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Cover - USD ($)
$ in Billions
 12 Months Ended
Sep. 30, 2025
Nov. 24, 2025
Mar. 28, 2025
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Sep. 30, 2025    
Current Fiscal Year End Date --09-30    
Document Transition Report false    
Entity File Number 001-37793    
Entity Registrant Name Atkore Inc.    
Entity Incorporation, State or Country Code DE    
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    
Title of 12(b) Security Common stock, par value $0.01 per share    
Trading Symbol ATKR    
Security Exchange Name NYSE    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Large Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
ICFR Auditor Attestation Flag true    
Document Financial Statement Error Correction [Flag] false    
Entity Shell Company false    
Entity Public Float     $ 1.9
Entity Common Stock, Shares Outstanding   33,750,486  
Documents Incorporated by Reference
Documents incorporated by reference:
Portions of the registrant's proxy statement to be filed with the United States Securities and Exchange Commission in connection with the registrant's 2026 annual meeting of stockholders (the "Proxy Statement") are incorporated by reference into Part III hereof. Such Proxy Statement will be filed within 120 days of the registrant's fiscal year ended September 30, 2025.
    
Entity Central Index Key 0001666138    
Document Fiscal Year Focus 2025    
Amendment Flag false    
Document Fiscal Period Focus FY