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, 2017	May 31, 2016	May 31, 2017	May 31, 2016	Aug. 31, 2016
Segment Reporting Information [Line Items]
Net sales		$ 1,382,616	$ 1,227,390	$ 3,607,300	$ 3,401,946
Adjusted operating profit (loss) from continuing operations		64,848	60,940	140,471	146,969
Total assets		3,274,599		3,274,599		$ 3,130,869
Continuing Operations
Segment Reporting Information [Line Items]
Net sales		1,382,616	1,227,390	3,607,300	3,401,946
Adjusted operating profit (loss) from continuing operations		64,848	60,940		146,969
Total assets	[1]	3,274,163		3,274,163		3,124,082
Americas Recycling
Segment Reporting Information [Line Items]
Net sales		247,896	156,352	590,760	430,829
Adjusted operating profit (loss) from continuing operations		9,286	(1,978)	11,954	(16,171)
Total assets	[1]	282,042		282,042		188,873
Americas Mills
Segment Reporting Information [Line Items]
Net sales		243,934	227,736	667,872	634,926
Adjusted operating profit (loss) from continuing operations		50,734	54,976	139,002	164,739
Total assets	[1]	919,923		919,923		798,481
Americas Fabrication
Segment Reporting Information [Line Items]
Net sales		377,188	382,607	1,013,847	1,096,049
Adjusted operating profit (loss) from continuing operations		1,808	22,794	9,025	58,964
Total assets	[1]	706,319		706,319		659,165
International Mill
Segment Reporting Information [Line Items]
Net sales		167,399	141,043	435,714	368,949
Adjusted operating profit (loss) from continuing operations		12,953	5,467	32,356	10,189
Total assets	[1]	431,284		431,284		372,492
International Marketing and Distribution
Segment Reporting Information [Line Items]
Net sales		344,290	315,067	891,606	867,084
Adjusted operating profit (loss) from continuing operations		10,164	892	15,341	(3,570)
Total assets	[1]	637,953		637,953		564,068
Corporate
Segment Reporting Information [Line Items]
Net sales		1,909	4,585	7,501	4,109
Adjusted operating profit (loss) from continuing operations		(20,880)	(22,542)	(67,210)	(69,415)
Total assets	[1]	871,040		871,040		1,034,053
Eliminations
Segment Reporting Information [Line Items]
Net sales		0	0	0	0
Adjusted operating profit (loss) from continuing operations		783	1,331	3	2,233
Total assets	[1]	(574,398)		(574,398)		(493,050)
Segments | Continuing Operations
Segment Reporting Information [Line Items]
Net sales		1,382,616	1,227,390	3,607,300	3,401,946
Adjusted operating profit (loss) from continuing operations				140,471
Segments | Americas Recycling
Segment Reporting Information [Line Items]
Net sales		294,166	182,477	694,202	510,030
Segments | Americas Mills
Segment Reporting Information [Line Items]
Net sales		427,276	396,481	1,151,034	1,117,442
Segments | Americas Fabrication
Segment Reporting Information [Line Items]
Net sales		379,976	385,080	1,022,202	1,103,538
Segments | International Mill
Segment Reporting Information [Line Items]
Net sales		167,629	141,438	436,335	369,344
Segments | International Marketing and Distribution
Segment Reporting Information [Line Items]
Net sales		347,113	319,604	897,568	879,517
Segments | Corporate
Segment Reporting Information [Line Items]
Net sales		1,909	4,585	7,501	4,109
Segments | Eliminations
Segment Reporting Information [Line Items]
Net sales		(235,453)	(202,275)	(601,542)	(582,034)
Intersegment | Continuing Operations
Segment Reporting Information [Line Items]
Net sales		0	0	0	0
Intersegment | Americas Recycling
Segment Reporting Information [Line Items]
Net sales		46,270	26,125	103,442	79,201
Intersegment | Americas Mills
Segment Reporting Information [Line Items]
Net sales		183,342	168,745	483,162	482,516
Intersegment | Americas Fabrication
Segment Reporting Information [Line Items]
Net sales		2,788	2,473	8,355	7,489
Intersegment | International Mill
Segment Reporting Information [Line Items]
Net sales		230	395	621	395
Intersegment | International Marketing and Distribution
Segment Reporting Information [Line Items]
Net sales		2,823	4,537	5,962	12,433
Intersegment | Corporate
Segment Reporting Information [Line Items]
Net sales		0	0	0	0
Intersegment | Eliminations
Segment Reporting Information [Line Items]
Net sales		(235,453)	$ (202,275)	(601,542)	$ (582,034)
Discontinued operations
Segment Reporting Information [Line Items]
Disposal Group, Including Discontinued Operation, Assets		$ 400		$ 400		$ 6,800

[1] Excludes total assets from discontinued operations of $0.4 million at May 31, 2017 and $6.8 million at August 31, 2016.