DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) $ / shares in Units, CAD in Thousands, AUD in Thousands	12 Months Ended
	Sep. 30, 2016 AUD component segment unit company	Sep. 30, 2016 USD ($) component segment unit company $ / shares	Sep. 30, 2016 CAD component segment unit company	Sep. 30, 2015 AUD	Sep. 30, 2015 USD ($) $ / shares	Sep. 30, 2015 CAD	Sep. 30, 2014 USD ($)
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Amount		$ 2,193,000
Number of operating segments | segment	3	3	3
Cash in non U.S. bank accounts		$ 24,000,000			$ 31,700,000
Debt instrument, interest rate, stated percentage		4.00%
Fair value of insurance contracts		$ 3,088,000
Proceeds from Sale of Trading Securities Held-for-investment		$ 1,000,000
Proceeds used to settle available-for-sale securities outstanding					8,891,000
Gain, net of tax, reclassified					$ 870,000
Contracts revenue | CAD			CAD 4,855			CAD 6,500
Contracts weighted average rate price (in Dollars per share) | $ / shares		$ 1.31			$ 1.33
Accumulated other comprehensive income (loss), foreign currency translation adjustment, net of tax		$ (42,894,000)			$ (60,178,000)
Gain (loss) on hedging activity		(752,000)
Foreign currency transaction gain (loss), realized		(157,000)			280,000
Defined benefit plan, fair value of plan assets		$ 144,316,000			144,625,000
Contract period	1 year	1 year	1 year
Income (loss) from operations		$ 103,507,000			101,017,000		$ 78,164,000
Provision for loss on contracts		4,700,000
Customer program reserves and cash discounts netted against accounts receivable		8,509,000			7,507,000
Costs in excess of billings, noncurrent		12,000,000			16,500,000
Unbilled contracts receivable		2,600,000			2,800,000
Depreciation, depletion and amortization, nonproduction		62,689,000			62,144,000		59,488,000
Accumulated capitalized interest costs		3,844,000			4,165,000		4,529,000
Original cost of fully depreciated property plant and equipment		$ 275,657,000
Description of fair value calculation	Griffon used five year projections and a 3.0% terminal value to which discount rates between 9% and 10% were applied to calculate each unit’s fair value.	Griffon used five year projections and a 3.0% terminal value to which discount rates between 9% and 10% were applied to calculate each unit’s fair value.	Griffon used five year projections and a 3.0% terminal value to which discount rates between 9% and 10% were applied to calculate each unit’s fair value.
Fair value projections	5 years	5 years	5 years
Fair value terminal value	3.00%	3.00%	3.00%
Goodwill, impairment loss		$ 0			0		0
Unrecognized tax benefits		5,955,000			7,851,000		7,906,000
Research and development arrangement, contract to perform for others, costs incurred, gross		26,200,000			25,600,000		23,400,000
Shipping, handling and transportation costs		36,900,000			40,800,000		42,400,000
Advertising revenue cost		22,000,000			24,000,000		24,000,000
Net cash used in financing activities		$ 8,888,000			(44,851,000)		(27,930,000)
Home & Building Products [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Number of companies | company	2	2	2
Income (loss) from operations		$ 79,682,000			58,883,000		40,538,000
Number of components | component	2	2	2
Number of reporting units | unit	1	1	1
Other Income [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Trading Securities, Realized Loss		$ 13,000
Recognized gain in other income					489,000
Selling, general and administrative expenses [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Depreciation		$ 13,239,000			13,009,000		10,815,000
U.S. Government [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Percentage of consolidated accounts receivable	16.00%	16.00%	16.00%
P & G [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Percentage of consolidated accounts receivable	7.00%	7.00%	7.00%
Home Depot [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Percentage of consolidated accounts receivable	14.00%	14.00%	14.00%
Contracts accounted for under percentage of completion [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Income (loss) from operations		$ (700,000)			$ (400,000)		$ (400,000)
Designated as hedging instrument [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Contracts revenue | AUD	AUD 25,500			AUD 25,531
Contracts weighted average rate price (in Dollars per share) | $ / shares		$ 1.30			$ 1.43
Accumulated other comprehensive income (loss), foreign currency translation adjustment, before tax		$ 1,545,000			$ 1,049,000
Accumulated other comprehensive income (loss), foreign currency translation adjustment, net of tax		1,004,000			682,000
Gain (loss) on hedging activity		(752,000)			1,223,000
Level 2 [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Defined benefit plan, fair value of plan assets		59,427,000			84,222,000
Level 2 [Member] | Estimate of fair value measurement [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Trading securities		1,314,000			1,374,000
Level 2 [Member] | Portion at other than fair value measurement [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Trading securities		1,000,000			1,000,000
Senior notes [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Long-term debt, fair value		725,000,000
Convert. debt due 2017 [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Long-term debt, fair value		$ 121,563,000
Maximum [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Maturity period of highly liquid investments	3 months	3 months	3 months
Contracts expiration days	270 days	270 days	270 days
Fair value discount rates	9.50%	9.50%	9.50%
Finite-lived intangible asset, useful life	25 years	25 years	25 years
Maximum [Member] | Building and building improvements [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Property, plant and equipment, useful life	40 years	40 years	40 years
Maximum [Member] | Machinery and equipment [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Property, plant and equipment, useful life	15 years	15 years	15 years
Minimum [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Contracts expiration days	14 days	14 days	14 days
Fair value discount rates	7.50%	7.50%	7.50%
Finite-lived intangible asset, useful life	8 years	8 years	8 years
Minimum [Member] | Building and building improvements [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Property, plant and equipment, useful life	25 years	25 years	25 years
Minimum [Member] | Machinery and equipment [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Property, plant and equipment, useful life	2 years	2 years	2 years
Canadian Dollar Forward Contracts [Member] | Level 2 [Member] | Not Designated as Hedging Instrument [Member] | Other Income [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Gain (Loss) on Sale of Derivatives		$ 136,000			257,000
Canadian Dollar Forward Contracts [Member] | Maximum [Member] | Not Designated as Hedging Instrument [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Foreign Currency Contracts Duration	270 days	270 days	270 days
Canadian Dollar Forward Contracts [Member] | Minimum [Member] | Not Designated as Hedging Instrument [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Foreign Currency Contracts Duration	14 days	14 days	14 days
Accounting Standards Update 2016-09, Statutory Tax Withholding Component [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Net cash provided by operating activities		$ 2,291,000
Net cash used in financing activities		$ 2,291,000
Accounting Standards Update 2015-17 [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Deferred tax assets, noncurrent					(3,793,000)
Deferred tax liabilities, noncurrent					$ (14,827,000)