DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) $ / shares in Units, CAD in Thousands, AUD in Thousands	12 Months Ended
	Sep. 30, 2015 AUD component segment unit company	Sep. 30, 2015 USD ($) component segment unit company $ / shares	Sep. 30, 2015 CAD component segment unit company	Sep. 30, 2014 AUD	Sep. 30, 2014 USD ($) $ / shares	Sep. 30, 2013 USD ($)
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Number of operating segments | segment	3	3	3
Number of companies | company	2	2	2
Cash in non U.S. bank accounts		$ 31,700,000			$ 34,500,000
Debt instrument, interest rate, stated percentage		4.00%
Fair value of insurance contracts		$ 2,942,000
Proceeds used to settle available-for-sale securities outstanding		8,891,000
Gain, net of tax, reclassified		$ 870,000
Contracts revenue			CAD 6,500	AUD 3,197
Contracts weighted average rate price (in Dollars per share) | $ / shares		$ 1.33			$ 1.14
Accumulated other comprehensive income (loss), foreign currency translation adjustment, net of tax		$ (60,178,000)			$ (3,820,000)
Gain (loss) on hedging activity		1,223,000			0	$ 0
Foreign currency transaction gain (loss), realized		(274,000)			(141,000)
Defined benefit plan, fair value of plan assets		$ 144,625,000			154,966,000
Contract period	1 year	1 year	1 year
Income (loss) from operations		$ 101,017,000			78,164,000	63,854,000
Provision for loss on contracts		10,600,000
Customer program reserves and cash discounts netted against accounts receivable		7,507,000			9,295,000
Costs in excess of billings, noncurrent		16,500,000			8,400,000
Unbilled contracts receivable		2,800,000			2,200,000
Depreciation, depletion and amortization, nonproduction		62,144,000			59,488,000	62,911,000
Accumulated capitalized interest costs		4,165,000			4,529,000	4,030,000
Original cost of fully depreciated property plant and equipment		$ 18,146,000
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		7,851,000			7,906,000	10,520,000
Research and development arrangement, contract to perform for others, costs incurred, gross		25,600,000			23,400,000	22,400,000
Shipping, handling and transportation costs		40,800,000			42,400,000	39,600,000
Advertising revenue cost		24,000,000			24,000,000	23,000,000
Home & Building Products [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Income (loss) from operations		$ 58,883,000			40,538,000	26,130,000
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]
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		$ 13,009,000			10,815,000	12,733,000
U.S. Government [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Percentage of consolidated accounts receivable	13.00%	13.00%	13.00%
P & G [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Percentage of consolidated accounts receivable	8.00%	8.00%	8.00%
Home Depot [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Percentage of consolidated accounts receivable	10.00%	10.00%	10.00%
Contracts accounted for under percentage of completion [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Income (loss) from operations		$ (400,000)			$ (400,000)	$ 3,400,000
Designated as hedging instrument [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Contracts revenue | AUD	AUD 25,531			AUD 4,975
Contracts weighted average rate price (in Dollars per share) | $ / shares		$ 1.43			$ 1.14
Accumulated other comprehensive income (loss), foreign currency translation adjustment, before tax		$ 1,049,000			$ 386,000
Accumulated other comprehensive income (loss), foreign currency translation adjustment, net of tax		682,000			252,000
Gain (loss) on hedging activity		1,223,000
Level 1 [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Defined benefit plan, fair value of plan assets		60,403,000			78,229,000
Level 1 [Member] | Estimate of fair value measurement [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Available-for-sale securities					9,770,000
Level 1 [Member] | Portion at other than fair value measurement [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Available-for-sale securities					8,400,000
Level 2 [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Defined benefit plan, fair value of plan assets		84,222,000			76,737,000
Level 2 [Member] | Estimate of fair value measurement [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Trading securities		1,374,000			1,274,000
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		570,000,000
Convert. debt due 2017 [Member]
DESCRIPTION OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) [Line Items]
Long-term debt, fair value		$ 118,875,000
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	360 days	360 days	360 days
Fair value discount rates	10.00%	10.00%	10.00%
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	30 days	30 days	30 days
Fair value discount rates	9.00%	9.00%	9.00%
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