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LONG-TERM DEBT - Narrative (Details) $ in Thousands			1 Months Ended			12 Months Ended
	Jun. 26, 2024 USD ($)	Jun. 24, 2024 USD ($)	Jul. 31, 2018 USD ($)	Jul. 31, 2018 GBP (£)	Nov. 30, 2012 CAD ($)	Sep. 30, 2025 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2025 CAD ($)	Sep. 30, 2025 AUD ($)	Sep. 30, 2024 AUD ($)	Jun. 25, 2024	Sep. 28, 2023 USD ($)	Aug. 01, 2023 USD ($)	Jul. 31, 2023 USD ($)	Jan. 24, 2022 USD ($)
Debt Instrument [Line Items]
Minimum payments under debt agreements for 2026						$ 8,103,000
Minimum payments under debt agreements for 2027						8,045,000
Minimum payments under debt agreements for 2028						982,819,000
Minimum payments under debt agreements for 2029						425,047,000
Minimum payments under debt agreements for 2030						12,000
Minimum payments under debt agreements thereafter						0
Capitalized fees & expenses						11,196,000	$ 15,203,000
Long-term debt, gross						1,424,026,000	1,539,685,000
Gain (loss) from debt extinguishment						0	(1,700,000)	$ (437,000)
Revolver due 2028
Debt Instrument [Line Items]
Maximum borrowing capacity																$ 500,000,000	$ 400,000,000
Letters of credit outstanding, amount						14,328,000
Line of credit facility, remaining borrowing capacity						$ 485,672,000
Revolver Due 2025, SOFR Loan
Debt Instrument [Line Items]
Debt instrument, interest rate at period end						5.98%					5.98%	5.98%
Revolver Due 2025, SONIA Loan
Debt Instrument [Line Items]
Debt instrument, interest rate at period end						5.75%					5.75%	5.75%
Revolver Due 2025, Base Rate Loan
Debt Instrument [Line Items]
Debt instrument, interest rate at period end						8.00%					8.00%	8.00%
Term Loan | Ames UK
Debt Instrument [Line Items]
Debt instrument, face amount | £				£ 14,000,000
Revolving Credit Facility | Ames UK
Debt Instrument [Line Items]
Debt instrument, face amount | £				5,000,000
Line of credit facility, amount outstanding																	0
Letter of Credit Subfacility | Revolver due 2028
Debt Instrument [Line Items]
Maximum borrowing capacity																125,000,000	100,000,000
Line of credit facility, incremental minimum borrowing amount																500,000,000	$ 375,000,000
Multicurrency Subfacility | Revolver due 2028
Debt Instrument [Line Items]
Maximum borrowing capacity																$ 200,000,000
Receivables Purchase Facility | Griffon Australia
Debt Instrument [Line Items]
Debt instrument, face amount													$ 15,000,000
Debt instrument, interest rate at period end						4.79%					4.79%	4.79%
Maximum borrowing capacity												$ 30,000,000	$ 30,000,000
Line of credit facility, remaining borrowing capacity						$ 19,707,000
Line of credit facility, amount outstanding						0
Senior Notes | Senior Notes due 2028
Debt Instrument [Line Items]
Debt instrument, face amount										$ 1,000,000,000
Stated percentage										5.75%
Capitalized fees & expenses										$ 16,448,000
Debt instrument, repurchased face amount									$ 25,225,000
Repurchase of debt instrument, discount rate									91.82%
Debt instrument, repurchase amount									$ 23,161,000
Debt issuance costs, net						4,880,000
Senior Notes | Senior Notes due 2028 | Quoted Prices in Active Markets for Identical Assets (Level 1)
Debt Instrument [Line Items]
Long-term debt, fair value						972,338,000
Senior Notes | Term Loan B due 2029
Debt Instrument [Line Items]
Repayments of debt										$ 1,000,000,000
Stated percentage										5.25%
Revolver due 2028
Debt Instrument [Line Items]
Capitalized fees & expenses						2,113,000	2,859,000
Long-term debt, gross						0	107,500,000
Term Loan B due 2029
Debt Instrument [Line Items]
Capitalized fees & expenses							5,420,000
Long-term debt, gross						449,000,000	$ 457,000,000
Term Loan B due 2029 | Quoted Prices in Active Markets for Identical Assets (Level 1)
Debt Instrument [Line Items]
Long-term debt, fair value						450,684,000
Term Loan | Ames UK
Debt Instrument [Line Items]
Repayments of debt			$ 9,543,000	7,525,000
Term Loan | Term Loan B due 2029
Debt Instrument [Line Items]
Debt instrument, face amount																		$ 800,000,000
Repayments of debt								325,000,000	325,000,000
Capitalized fees & expenses						$ 4,169,000
Issuance price, percentage																		99.75%
Gain (loss) from debt extinguishment								(437,000)	(6,296,000)
Write off of deferred debt issuance cost, underwriting and other fees								386,000	5,575,000
Write off of deferred debt issuance cost, original issuer discount								$ 51,000	$ 721,000
S0FR floor rate	0.00%													0.50%
Debt instrument, charges for debt amendment	$ 1,700,000
Debt instrument, interest rate at period end						6.13%					6.13%	6.13%
Debt instrument, periodic payment, principal		$ 2,000,000
Non U.S. lines of credit
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate					1.20%
Maximum borrowing capacity					$ 15,000
Line of credit facility, remaining borrowing capacity						$ 14,376,000					$ 20,000
Line of credit facility, amount outstanding						$ 0
Mortgages | Ames UK
Debt Instrument [Line Items]
Debt instrument, face amount | £				4,000,000
Repayments of debt			$ 3,108,000	£ 2,451,000
Secured Overnight Financing Rate | Revolver Due 2025, SOFR Loan
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate						1.75%
Secured Overnight Financing Rate | Term Loan | Term Loan B due 2029
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate, period increase (decrease)	(0.25%)
Debt instrument, basis spread on variable rate	2.00%
Base Rate | Revolver Due 2025, Base Rate Loan
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate						0.75%
Canada Dollar Offer Rate | Non U.S. lines of credit
Debt Instrument [Line Items]
Line of credit facility, interest rate at period end						4.06%					4.06%	4.06%
Bank Bill Swap Bid Rate | Receivables Purchase Facility | Griffon Australia
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate						1.25%
Sterling Overnight Index Average | Revolver Due 2025, SONIA Loan
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate						1.75%
Ocala, Florida | Finance lease - real estate
Debt Instrument [Line Items]
Payment to acquire leased property															$ 23,207,000
Long-term debt, percentage bearing fixed interest, percentage rate															5.60%

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