BUSINESS SEGMENTS (Summary of Certain Financial Information from Continuing Operations by Reportable Segment) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Feb. 28, 2018	Feb. 28, 2017	Feb. 28, 2018	Feb. 28, 2017	Aug. 31, 2017
Segment Reporting Information [Line Items]
Net sales		$ 1,054,268	$ 862,298	$ 2,130,801	$ 1,715,226
Adjusted operating profit (loss) from continuing operations		18,886	43,404	66,051	65,076
Total assets		2,910,480		2,910,480		$ 2,975,131
Continuing Operations
Segment Reporting Information [Line Items]
Net sales		1,054,268	862,298	2,130,801	1,715,226
Adjusted operating profit (loss) from continuing operations		18,886	43,404		65,076
Total assets	[1]	2,766,980		2,766,980		2,681,531
Americas Recycling
Segment Reporting Information [Line Items]
Net sales		265,432	188,502	539,769	342,864
Adjusted operating profit (loss) from continuing operations		12,238	7,788	22,230	2,734
Total assets	[1]	298,470		298,470		240,371
Americas Mills
Segment Reporting Information [Line Items]
Net sales		262,703	220,607	509,436	423,938
Adjusted operating profit (loss) from continuing operations		31,536	51,319	72,300	88,268
Total assets	[1]	1,032,112		1,032,112		933,022
Americas Fabrication
Segment Reporting Information [Line Items]
Net sales		310,199	301,382	640,751	636,659
Adjusted operating profit (loss) from continuing operations		(27,117)	507	(31,900)	7,218
Total assets	[1]	671,142		671,142		683,609
International Mill
Segment Reporting Information [Line Items]
Net sales		211,484	134,472	431,696	269,004
Adjusted operating profit (loss) from continuing operations		24,490	9,484	47,927	19,546
Total assets	[1]	511,140		511,140		464,428
Corporate
Segment Reporting Information [Line Items]
Net sales		4,450	17,335	9,149	42,761
Adjusted operating profit (loss) from continuing operations		(22,361)	(25,112)	(43,034)	(51,895)
Total assets	[1]	695,856		695,856		687,984
Eliminations
Segment Reporting Information [Line Items]
Net sales		0	0	0	0
Adjusted operating profit (loss) from continuing operations		100	(582)	(1,472)	(795)
Total assets	[1]	(441,740)		(441,740)		(327,883)
Segments | Continuing Operations
Segment Reporting Information [Line Items]
Net sales		1,054,268	862,298	2,130,801	1,715,226
Adjusted operating profit (loss) from continuing operations				66,051
Segments | Americas Recycling
Segment Reporting Information [Line Items]
Net sales		320,627	223,328	639,968	400,036
Segments | Americas Mills
Segment Reporting Information [Line Items]
Net sales		425,887	376,593	839,405	723,758
Segments | Americas Fabrication
Segment Reporting Information [Line Items]
Net sales		312,973	303,826	645,752	642,225
Segments | International Mill
Segment Reporting Information [Line Items]
Net sales		211,765	134,652	432,242	269,395
Segments | Corporate
Segment Reporting Information [Line Items]
Net sales		4,450	17,335	9,149	43,402
Segments | Eliminations
Segment Reporting Information [Line Items]
Net sales		(221,434)	(193,436)	(435,715)	(363,590)
Intersegment | Continuing Operations
Segment Reporting Information [Line Items]
Net sales		0	0	0	0
Intersegment | Americas Recycling
Segment Reporting Information [Line Items]
Net sales		55,195	34,826	100,199	57,172
Intersegment | Americas Mills
Segment Reporting Information [Line Items]
Net sales		163,184	155,986	329,969	299,820
Intersegment | Americas Fabrication
Segment Reporting Information [Line Items]
Net sales		2,774	2,444	5,001	5,566
Intersegment | International Mill
Segment Reporting Information [Line Items]
Net sales		281	180	546	391
Intersegment | Corporate
Segment Reporting Information [Line Items]
Net sales		0	0	0	641
Intersegment | Eliminations
Segment Reporting Information [Line Items]
Net sales		(221,434)	$ (193,436)	(435,715)	$ (363,590)
Discontinued operations
Segment Reporting Information [Line Items]
Assets from discontinued operations		$ 143,500		$ 143,500		$ 293,600

[1] Excludes total assets from discontinued operations of $143.5 million at February 28, 2018 and $293.6 million at August 31, 2017.