BUSINESS SEGMENTS (Summary of Certain Financial Information from Continuing Operations by Reportable Segment and Major Product) (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended		9 Months Ended
	Feb. 28, 2021	May 31, 2020	Feb. 29, 2020	Feb. 28, 2021	Feb. 29, 2020	May 31, 2020	Aug. 31, 2020
Segment Reporting Information [Line Items]
Net sales	$ 1,462,270		$ 1,340,963	$ 2,854,073	$ 2,725,671
Adjusted EBITDA from continuing operations	141,733		137,721	285,366	297,526
Total assets	4,064,041			4,064,041			$ 4,081,728
Segments | Continuing Operations
Segment Reporting Information [Line Items]
Net sales	1,462,270		1,340,963	2,854,073	2,725,671
Adjusted EBITDA from continuing operations	141,733	$ 137,721		285,366		$ 297,526
Total assets	4,064,041			4,064,041			4,081,728
Segments | North America
Segment Reporting Information [Line Items]
Net sales	1,257,486		1,161,283	2,452,499	2,378,003
Adjusted EBITDA from continuing operations	171,612	152,831		327,246		327,563
Total assets	2,957,534			2,957,534			2,862,805
Segments | Europe
Segment Reporting Information [Line Items]
Net sales	202,066		180,079	396,662	345,468
Adjusted EBITDA from continuing operations	16,107	13,451		30,577		24,810
Total assets	566,195			566,195			532,850
Segments | Unaffiliated Customers
Segment Reporting Information [Line Items]
Net sales	1,462,270		1,340,963	2,854,073	2,725,671
Segments | Unaffiliated Customers | North America
Segment Reporting Information [Line Items]
Net sales	1,257,486		1,161,283	2,452,499	2,378,003
Segments | Unaffiliated Customers | Europe
Segment Reporting Information [Line Items]
Net sales	201,559		179,656	395,744	344,696
Segments | Raw material products
Segment Reporting Information [Line Items]
Net sales	259,787		195,720	472,854	379,548
Segments | Raw material products | North America
Segment Reporting Information [Line Items]
Net sales	255,012		193,312	465,249	374,935
Segments | Raw material products | Europe
Segment Reporting Information [Line Items]
Net sales	4,775		2,408	7,605	4,613
Segments | Steel Products
Segment Reporting Information [Line Items]
Net sales	671,683		585,173	1,280,795	1,156,080
Segments | Steel Products | North America
Segment Reporting Information [Line Items]
Net sales	514,201		437,648	971,858	878,811
Segments | Steel Products | Europe
Segment Reporting Information [Line Items]
Net sales	157,482		147,525	308,937	277,269
Segments | Downstream products
Segment Reporting Information [Line Items]
Net sales	434,159		465,523	905,661	993,450
Segments | Downstream products | North America
Segment Reporting Information [Line Items]
Net sales	400,397		441,765	837,426	941,492
Segments | Downstream products | Europe
Segment Reporting Information [Line Items]
Net sales	33,762		23,758	68,235	51,958
Segments | Other
Segment Reporting Information [Line Items]
Net sales	96,641		94,547	194,763	196,593
Segments | Other | North America
Segment Reporting Information [Line Items]
Net sales	87,876		88,558	177,966	182,765
Segments | Other | Europe
Segment Reporting Information [Line Items]
Net sales	5,540		5,965	10,967	10,856
Segments | Corporate
Segment Reporting Information [Line Items]
Net sales	2,718			4,912
Adjusted EBITDA from continuing operations	(45,986)
Total assets	540,312			540,312
Segments | Corporate | Unaffiliated Customers
Segment Reporting Information [Line Items]
Net sales	3,225		24	5,830	2,972
Segments | Corporate | Raw material products
Segment Reporting Information [Line Items]
Net sales	0		0	0	0
Segments | Corporate | Steel Products
Segment Reporting Information [Line Items]
Net sales	0		0	0	0
Segments | Corporate | Downstream products
Segment Reporting Information [Line Items]
Net sales	0		0	0	0
Segments | Corporate | Other
Segment Reporting Information [Line Items]
Net sales	3,225		24	5,830	2,972
Segments | Corporate and Other
Segment Reporting Information [Line Items]
Net sales			(399)		2,200
Adjusted EBITDA from continuing operations		$ (28,561)		(72,457)		$ (54,847)
Total assets							$ 686,073
Intersegment
Segment Reporting Information [Line Items]
Net sales	0		0	0	0
Intersegment | North America
Segment Reporting Information [Line Items]
Net sales	0		0	0	0
Intersegment | Europe
Segment Reporting Information [Line Items]
Net sales	507		423	918	772
Intersegment | Corporate
Segment Reporting Information [Line Items]
Net sales	$ (507)		$ (423)	$ (918)	$ (772)