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SCHEDULE I - CONDENSED FINANCIAL INFORMATION - Narrative (Details) - USD ($) $ in Thousands, shares in Millions			12 Months Ended
	Apr. 09, 2014	Mar. 06, 2014	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023	Dec. 22, 2010
Condensed Financial Statements, Captions [Line Items]
Payment to redeem shares	$ 250,000
Parent Company
Condensed Financial Statements, Captions [Line Items]
Distribution received from subsidiary			$ 150,444	$ 433,325	$ 491,033
Common Stock
Condensed Financial Statements, Captions [Line Items]
Non-binding letter of intent to acquire common stock (in shares)		40.3
Expense related to share redemption	$ 2,000
Atkore International | CD&R
Condensed Financial Statements, Captions [Line Items]
Preferred stock, percentage of outstanding capital stock (on an as-converted basis) (%)						51.00%
Common stock, percentage of outstanding capital stock (%)						49.00%

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