BUSINESS SEGMENTS (Summary of Certain Financial Information from Continuing Operations by Reportable Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	May 31, 2018	May 31, 2017	May 31, 2018	May 31, 2017	Aug. 31, 2017
Segment Reporting Information [Line Items]
Net sales	$ 1,204,484	$ 1,044,713	$ 3,335,285	$ 2,759,939
Adjusted operating profit (loss) from continuing operations	67,409	55,251	133,460	120,327
Total assets	3,245,493		3,245,493		$ 2,975,131
Continuing Operations
Segment Reporting Information [Line Items]
Net sales	1,204,484	1,044,713	3,335,285	2,759,939
Adjusted operating profit (loss) from continuing operations	67,409	55,251	133,460	120,327
Total assets	3,211,453		3,211,453		2,681,531
Americas Recycling
Segment Reporting Information [Line Items]
Net sales	292,679	247,896	832,448	590,760
Adjusted operating profit (loss) from continuing operations	14,350	9,247	36,580	11,981
Total assets	310,513		310,513		240,371
Americas Mills
Segment Reporting Information [Line Items]
Net sales	332,459	243,934	841,895	667,872
Adjusted operating profit (loss) from continuing operations	70,404	50,734	142,639	139,002
Total assets	1,078,308		1,078,308		933,022
Americas Fabrication
Segment Reporting Information [Line Items]
Net sales	375,183	377,188	1,015,934	1,013,847
Adjusted operating profit (loss) from continuing operations	(16,096)	1,808	(47,995)	9,025
Total assets	684,929		684,929		683,609
International Mill
Segment Reporting Information [Line Items]
Net sales	201,438	167,409	633,134	436,413
Adjusted operating profit (loss) from continuing operations	24,370	12,971	72,297	32,517
Total assets	476,946		476,946		464,428
Corporate
Segment Reporting Information [Line Items]
Net sales	2,725	8,286	11,874	51,047
Adjusted operating profit (loss) from continuing operations	(22,678)	(20,281)	(65,648)	(72,176)
Total assets	1,128,360		1,128,360		687,984
Eliminations
Segment Reporting Information [Line Items]
Net sales	0	0	0	0
Adjusted operating profit (loss) from continuing operations	(2,941)	772	(4,413)	(22)
Total assets	(467,603)		(467,603)		(327,883)
Segments | Continuing Operations
Segment Reporting Information [Line Items]
Net sales	1,204,484	1,044,713	3,335,285	2,759,939
Segments | Americas Recycling
Segment Reporting Information [Line Items]
Net sales	364,098	294,166	1,004,066	694,202
Segments | Americas Mills
Segment Reporting Information [Line Items]
Net sales	553,063	427,276	1,392,468	1,151,034
Segments | Americas Fabrication
Segment Reporting Information [Line Items]
Net sales	378,241	379,976	1,023,993	1,022,202
Segments | International Mill
Segment Reporting Information [Line Items]
Net sales	201,737	167,639	633,980	437,034
Segments | Corporate
Segment Reporting Information [Line Items]
Net sales	2,725	8,289	11,874	51,690
Segments | Eliminations
Segment Reporting Information [Line Items]
Net sales	(295,380)	(232,633)	(731,096)	(596,223)
Intersegment | Continuing Operations
Segment Reporting Information [Line Items]
Net sales	0	0	0	0
Intersegment | Americas Recycling
Segment Reporting Information [Line Items]
Net sales	71,419	46,270	171,618	103,442
Intersegment | Americas Mills
Segment Reporting Information [Line Items]
Net sales	220,604	183,342	550,573	483,162
Intersegment | Americas Fabrication
Segment Reporting Information [Line Items]
Net sales	3,058	2,788	8,059	8,355
Intersegment | International Mill
Segment Reporting Information [Line Items]
Net sales	299	230	846	621
Intersegment | Corporate
Segment Reporting Information [Line Items]
Net sales	0	3	0	643
Intersegment | Eliminations
Segment Reporting Information [Line Items]
Net sales	(295,380)	$ (232,633)	(731,096)	$ (596,223)
Discontinued operations
Segment Reporting Information [Line Items]
Assets from discontinued operations	$ 34,000		$ 34,000		$ 293,600