SHAREHOLDERS' EQUITY (Details)						3 Months Ended				9 Months Ended		12 Months Ended	83 Months Ended
	May 03, 2018 $ / shares	Jan. 17, 2017 USD ($) shares	Jul. 14, 2016 USD ($)	Jan. 29, 2016 shares	Dec. 10, 2013 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) senior_executive $ / shares shares	Sep. 30, 2017 $ / shares	Jun. 30, 2017 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) $ / shares shares	Jun. 30, 2017 USD ($) $ / shares	Sep. 30, 2017 $ / shares	Jun. 30, 2018 USD ($) $ / shares shares	Aug. 01, 2018 USD ($)	Jan. 31, 2018 shares	Oct. 02, 2017	Aug. 31, 2016 USD ($)	Aug. 03, 2016 USD ($)	Mar. 31, 2016 USD ($)	Sep. 30, 2015 USD ($)	Feb. 27, 2014 USD ($)	Dec. 21, 2009 USD ($)	Dec. 31, 2008 shares
SHAREHOLDERS' EQUITY (Details) [Line Items]
Common stock, dividends, per share, cash paid (in Dollars per share) | $ / shares						$ 1.07	$ 1.07	$ 0.06	$ 0.06	$ 1.21	$ 0.18	$ 0.24
Common Stock, Dividends, Per Share, Cash Paid, Total Up To Date | $ / shares										$ 1.21
Dividends declared, amount per share (in Dollars per share) | $ / shares	$ 0.07
Share-based compensation arrangement by share-based payment award, description										Options granted under the Incentive Plan may be either “incentive stock options” or nonqualified stock options, generally expire ten years after the date of grant and are granted at an exercise price of not less than 100% of the fair market value at the date of grant.
Share-based compensation arrangement by share-based payment award, expiration period										10 years
Maximum percentage of exercise price at grand date fair value										100.00%
Stock-based compensation						$ 2,452,000			$ 2,405,000	$ 7,372,000	$ 7,200,000
Shares paid for tax withholding for share based compensation (in Shares) | shares						1,592				199,044
Shares paid for tax withholding for share based compensation, value						$ 33,000				$ 4,478,000
Shares paid for tax withholding for share based compensation, value per share (in Dollars per share) | $ / shares						$ 20.85				$ 22.50
Face amount																	$ 35,092,000		$ 8,000,000	$ 32,280,000
Stock repurchase program, authorized amount					$ 50,000,000													$ 50,000,000
Stock repurchase program, remaining authorized repurchase amount						$ 8,327,000				$ 8,327,000			$ 8,327,000
Stock repurchased during period (in shares) | shares					4,444,444	650,500				2,088,739			22,518,037
Stock repurchased during period, value						$ 12,694,000				$ 41,110,000			$ 302,730,000
Stock repurchased during period per share (in Dollars per share) | $ / shares					$ 11.25	$ 19.51				$ 19.68			$ 13.44
Remaining number of shares authorized to be repurchased | shares					5,583,375,000
Incentive Stock Options [Member]
SHAREHOLDERS' EQUITY (Details) [Line Items]
Number of shares available for grant (in Shares) | shares						1,200,755				1,200,755			1,200,755
2006 Equity Incentive Plan [Member]
SHAREHOLDERS' EQUITY (Details) [Line Items]
Share based compensation arrangement by share based payment award equity instruments other than options additional grants in future (in Shares) | shares						0				0			0
Restricted Stock and Restricted Stock Units [Member]
SHAREHOLDERS' EQUITY (Details) [Line Items]
Equity instruments other than options, grants in period (in Shares) | shares							1,008,756
Performance Shares [Member]
SHAREHOLDERS' EQUITY (Details) [Line Items]
Award vesting period						3 years	3 years
Equity instruments other than options, grants in period (in Shares) | shares						250,170	480,756
Equity instruments other than options, vested in period, fair value						$ 4,739,000	$ 9,980,000
Equity instruments other than options, grants in period, weighted average grant date fair value (in Dollars per share) | $ / shares						$ 18.94	$ 20.76
Restricted Stock and Performance Shares [Member]
SHAREHOLDERS' EQUITY (Details) [Line Items]
Equity instruments other than options, grants in period (in Shares) | shares							528,000
Minimum [Member] | Restricted Stock [Member]
SHAREHOLDERS' EQUITY (Details) [Line Items]
Award vesting period										3 years
Maximum [Member] | Restricted Stock [Member]
SHAREHOLDERS' EQUITY (Details) [Line Items]
Award vesting period										4 years
Executive Officer [Member] | Restricted Stock [Member]
SHAREHOLDERS' EQUITY (Details) [Line Items]
Award vesting period							4 years
Equity instruments other than options, vested in period, fair value							$ 7,008,000
Equity instruments other than options, grants in period, weighted average grant date fair value (in Dollars per share) | $ / shares							$ 13.27
Number of persons granted shares | senior_executive							2
Award post-vesting holding period							2 years
Executive Officer [Member] | Minimum [Member] | Restricted Stock [Member]
SHAREHOLDERS' EQUITY (Details) [Line Items]
Awards vested in period (in shares) | shares							384,000
Executive Officer [Member] | Maximum [Member] | Restricted Stock [Member]
SHAREHOLDERS' EQUITY (Details) [Line Items]
Awards vested in period (in shares) | shares							528,000
Convert. debt due 2017 [Member]
SHAREHOLDERS' EQUITY (Details) [Line Items]
Face amount																						$ 100,000,000
Debt instrument, interest rate, stated percentage																						4.00%
Senior Notes 2022 [Member]
SHAREHOLDERS' EQUITY (Details) [Line Items]
Face amount																					$ 600,000,000
Debt instrument, interest rate, stated percentage																5.25%					5.25%
Debt conversion, original debt, amount			$ 125,000,000
Convertible Notes 2017 [Member]
SHAREHOLDERS' EQUITY (Details) [Line Items]
Debt conversion, converted instrument, amount		$ 173,855,000							173,855,000
Debt conversion, converted instrument, cash received		125,000,000							$ 125,000,000
Issuance of treasury stock in settlement of convertible debt		$ 48,858,000
Debt conversion, converted instrument, shares issued | shares		1,954,993							1,954,993
Subsequent Event [Member]
SHAREHOLDERS' EQUITY (Details) [Line Items]
Stock repurchase program, authorized amount														$ 50,000,000
Incentive Plan [Member]
SHAREHOLDERS' EQUITY (Details) [Line Items]
Number of shares authorized for award (in Shares) | shares				3,350,000											1,000,000
New shares issued (in Shares) | shares				600,000
Griffon Board Of Directors Program [Member]
SHAREHOLDERS' EQUITY (Details) [Line Items]
Stock repurchased during period (in shares) | shares													18,073,593
Stock repurchased during period, value													$ 252,730,000
Stock repurchased during period per share (in Dollars per share) | $ / shares													$ 13.98
GS Direct [Member]
SHAREHOLDERS' EQUITY (Details) [Line Items]
Investment Owned, Balance, Shares | shares																							10,000,000
Dividend Paid [Member]
SHAREHOLDERS' EQUITY (Details) [Line Items]
Common stock, dividends, per share, cash paid (in Dollars per share) | $ / shares						0.07
Special Dividends [Member]
SHAREHOLDERS' EQUITY (Details) [Line Items]
Common stock, dividends, per share, cash paid (in Dollars per share) | $ / shares						$ 1.00