SCHEDULE II — VALUATION AND QUALIFYING ACCOUNTS AND RESERVES (Narrative) (Details) (Allowance for doubtful accounts, USD $) In Thousands, unless otherwise specified	12 Months Ended
Aug. 31, 2014	Aug. 31, 2013	Aug. 31, 2012
Allowance for doubtful accounts
Valuation and Qualifying Accounts Disclosure [Line Items]
Amounts reclassified to the fair value of the deferred purchase price	$ (1,010)	$ (1,163)	$ (5,864)

Valuation allowances and reserves reclassified to fair value of deferred purchase price.

No definition available.

Name:	cmc_ValuationAllowancesAndReservesChargedReclassifiedToFairValueOfDeferredPurchasePrice
Namespace Prefix:	cmc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration