BUSINESS SEGMENTS (Summary of Certain Financial Information from Continuing Operations by Reportable Segment) (Details) - USD ($) $ in Thousands		3 Months Ended															12 Months Ended
		Aug. 31, 2019		May 31, 2019	[1]	Feb. 28, 2019	[1]	Nov. 30, 2018	[1]	Aug. 31, 2018	May 31, 2018	[1]	Feb. 28, 2018	[1]	Nov. 30, 2017	[1]	Aug. 31, 2019	Aug. 31, 2018	Aug. 31, 2017
Segment Reporting Information [Line Items]
Net sales		$ 1,543,005	[1]	$ 1,605,872		$ 1,402,783		$ 1,277,342		$ 1,308,438	$ 1,204,484		$ 1,054,268		$ 1,076,533		$ 5,829,002	$ 4,643,723	$ 3,844,069
Adjusted operating profit (loss)																	424,085	352,221	235,822
Interest expense																	71,373	40,957	44,151
Capital expenditures																	138,836	174,655	213,120
Depreciation and amortization																	158,652	131,508	124,490
Impairment of assets																	384	14,372	1,730
Total assets		3,758,771								3,328,304							3,758,771	3,328,304
Continuing Operations
Segment Reporting Information [Line Items]
Net sales																	5,829,002	4,643,723	3,844,069
Americas Recycling
Segment Reporting Information [Line Items]
Net sales																	908,451	1,117,714	865,462
Americas Mills
Segment Reporting Information [Line Items]
Net sales																	1,882,994	1,204,181	917,689
Americas Fabrication
Segment Reporting Information [Line Items]
Net sales																	2,209,671	1,416,572	1,364,826
International Mill
Segment Reporting Information [Line Items]
Net sales																	815,723	885,919	636,402
Corporate
Segment Reporting Information [Line Items]
Net sales																	12,163	19,337	59,690
Segments | Continuing Operations
Segment Reporting Information [Line Items]
Net sales																	5,829,002	4,643,723	3,844,069
Adjusted operating profit (loss)																	424,085	352,221	235,822
Interest expense	[2]																71,373	40,957	44,151
Capital expenditures																	138,836	171,367	213,074
Impairment of assets																	384	14,372	1,730
Total assets	[3]	3,758,771								3,328,304							3,758,771	3,328,304	2,975,131
Segments | Americas Recycling
Segment Reporting Information [Line Items]
Net sales																	1,146,546	1,365,429	1,011,500
Adjusted operating profit (loss)																	42,124	68,694	33,541
Interest expense	[2]																3,097	3,605	2,979
Capital expenditures																	22,560	8,592	7,148
Depreciation and amortization																	16,825	17,246	15,501
Impairment of assets																	0	180	559
Total assets	[3]	257,517								291,838							257,517	291,838	240,371
Segments | Americas Mills
Segment Reporting Information [Line Items]
Net sales																	3,068,274	1,996,903	1,565,454
Adjusted operating profit (loss)																	545,215	301,805	224,183
Interest expense	[2]																16,186	5,317	(3,394)
Capital expenditures																	54,069	121,029	172,738
Depreciation and amortization																	91,326	61,512	49,419
Impairment of assets																	0	8	0
Total assets	[3]	1,667,366								1,115,339							1,667,366	1,115,339	933,022
Segments | Americas Fabrication
Segment Reporting Information [Line Items]
Net sales																	2,223,379	1,427,882	1,375,928
Adjusted operating profit (loss)																	(123,014)	(39,394)	27,259
Interest expense	[2]																27,656	14,295	9,899
Capital expenditures																	12,490	14,386	15,495
Depreciation and amortization																	17,567	13,537	13,400
Impairment of assets																	369	14,157	0
Total assets	[3]	1,106,420								739,151							1,106,420	739,151	683,609
Segments | International Mill
Segment Reporting Information [Line Items]
Net sales																	817,048	887,038	637,273
Adjusted operating profit (loss)																	100,102	131,720	76,068
Interest expense	[2]																2,493	2,699	3,079
Capital expenditures																	40,337	23,552	12,603
Depreciation and amortization																	25,993	27,255	25,830
Impairment of assets																	15	27	150
Total assets	[3]	464,177								485,548							464,177	485,548	464,428
Segments | Corporate
Segment Reporting Information [Line Items]
Net sales																	(1,426,245)	(1,033,529)	(746,086)
Adjusted operating profit (loss)																	(140,342)	(110,604)	(125,229)
Interest expense	[2]																21,941	15,041	31,588
Capital expenditures																	9,380	3,808	5,090
Depreciation and amortization																	6,941	11,958	20,340
Impairment of assets																	0	0	1,021
Total assets	[3]	$ 263,291								$ 696,428							263,291	696,428	653,701
Intersegment | Continuing Operations
Segment Reporting Information [Line Items]
Net sales																	0	0	0
Intersegment | Americas Recycling
Segment Reporting Information [Line Items]
Net sales																	238,095	247,715	146,038
Intersegment | Americas Mills
Segment Reporting Information [Line Items]
Net sales																	1,185,280	792,722	647,765
Intersegment | Americas Fabrication
Segment Reporting Information [Line Items]
Net sales																	13,708	11,310	11,102
Intersegment | International Mill
Segment Reporting Information [Line Items]
Net sales																	1,325	1,119	871
Intersegment | Corporate
Segment Reporting Information [Line Items]
Net sales																	$ (1,438,408)	$ (1,052,866)	$ (805,776)

[1] Excludes discontinued operations.

[2] Includes intercompany interest expense (income) in the segments, which is eliminated within Corporate and Other.

[3] Total assets listed in Corporate and Other includes assets from discontinued operations