Stockholders' Equity And Earnings Per Share Attributable To CMC (Reconciliation of the Denominators of the Earnings Per Share Calculations) (Details)	3 Months Ended	9 Months Ended
May 31, 2012	May 31, 2011	May 31, 2012	May 31, 2011
Reconciliation of the denominators of the earnings per share
Shares outstanding for basic earnings per share	115,946,691	115,403,374	115,726,793	114,819,792
Stock based incentive/purchase plans	988,149	957,381	1,015,800	1,217,638
Shares outstanding for diluted earnings per share	116,934,840	116,360,755	116,742,593	116,037,430

The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef

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