STOCKHOLDERS’ EQUITY AND EARNINGS PER SHARE ATTRIBUTABLE TO CMC (Narrative) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Feb. 28, 2017	Feb. 29, 2016	Feb. 28, 2017	Feb. 29, 2016	Nov. 30, 2014
Earnings Per Share [Abstract]
Stock repurchase program, authorized amount					$ 100,000,000.0
Stock repurchase program, shares purchased (shares)	0	1,938,983	0	2,255,069
Stock repurchase program, average purchase price per share (in USD per share)		$ 13.43		$ 13.57
Stock repurchase program, remaining authorized repurchase amount	$ 27,600,000		$ 27,600,000