STOCKHOLDERS’ EQUITY AND EARNINGS PER SHARE ATTRIBUTABLE TO CMC (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
Nov. 30, 2014	Oct. 27, 2014
Earnings Per Share [Abstract]
Stock repurchase program, authorized amount		$ 100.0
Stock repurchase program, shares purchased	560,493us-gaap_TreasuryStockSharesAcquired
Stock repurchase program, average purchase price per share	$ 16.67
Stock repurchase program, remaining authorized repurchase amount	$ 90.7

Number of shares that have been repurchased during the period and are being held in treasury.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29, 30

-Article 5

Name:	us-gaap_TreasuryStockSharesAcquired
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration