Segment Reporting [Abstract] Statement [Table] Statement [Table] Statement, Operating Activities Segment [Axis] Statement, Operating Activities Segment [Axis] Segment, Operating Activities [Domain] Segment, Operating Activities [Domain] Segment, Discontinued Operations [Member] Segment, Discontinued Operations [Member] Statement [Line Items] Statement [Line Items] Number of Operating Segments Number of Operating Segments Total assets Assets of Disposal Group, Including Discontinued Operation Goodwill and Intangible Assets Disclosure [Abstract] Schedule of Goodwill [Table] Schedule of Goodwill [Table] Business Segments [Axis] Business Segments [Axis] Segment [Domain] Segment [Domain] Americas Recycling [Member] Americas Recycling [Member] Americas recycling. Americas Mills [Member] Americas Mills [Member] Americas mills. Americas Fabrication [Member] Americas Fabrication [Member] Americas fabrication. International Mill [Member] International Mills [Member] International mill. International Marketing and Distribution [Member] International Marketing And Distribution [Member] International marketing and distribution. Goodwill [Line Items] Goodwill [Line Items] Goodwill [Roll Forward] Goodwill [Roll Forward] Balance at August 31, 2012 Goodwill Translation Goodwill, Translation Adjustments Balance at November 30, 2012 Discontinued Operations and Disposal Groups [Abstract] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Table] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Table] Disposal Group Name [Axis] Disposal Group Name [Axis] Disposal Groups, Including Discontinued Operations, Name [Domain] Disposal Groups, Including Discontinued Operations, Name [Domain] CMCS [Member] Cmcs [Member] CMC Sisak Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Severance expense Severance Costs Business Divestiture Disposal Price Business Divestiture Disposal Price This represents disposal price of a business unit or asset during divestiture. Fair Value Disclosures [Abstract] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair value, inputs, level 1 [Member] Fair Value, Inputs, Level 1 [Member] Fair value, inputs, level 2 [Member] Fair Value, Inputs, Level 2 [Member] Fair value, inputs, level 3 [Member] Fair Value, Inputs, Level 3 [Member] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Fair value, measurements, recurring [Member] Fair Value, Measurements, Recurring [Member] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Money market investments Cash and Cash Equivalents, Fair Value Disclosure Derivative assets Derivative Asset, Fair Value, Gross Asset Nonqualified benefit plan assets Nonqualified Benefit Plan Assets Fair Value Disclosure This represents fair value of assets associated with nonqualified benefit plan presented on a gross basis. Derivative liabilities Derivative Liability, Fair Value, Gross Liability Nonqualified benefit plan liabilities Nonqualified Benefit Plan Liabilities Fair Value Disclosure This represents fair value of liabilities associated with nonqualified benefit plan presented on a gross basis. Discontinued operations Disposal Groups, Including Discontinued Operations, Disclosure [Text Block] Earnings Per Share [Abstract] Stockholders' equity and earnings per share attributable to CMC Earnings Per Share [Text Block] Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Award Type [Axis] Award Type [Axis] Award Type [Domain] Award Type [Domain] RSUs and PSUs excluding cash components [Member] RSUs And PSUs Excluding Cash Components [Member] [Member] RSUs And PSUs Excluding Cash Components [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Restricted stock awards and PSUs, outstanding, number, beginning balance Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Restricted stock awards and PSUs, granted, number Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Restricted stock awards and PSUs, vested, number Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Restricted stock awards and PSUs, forfeited, number Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Restricted stock awards and PSUs, outstanding, number, ending balance Restricted stock awards and PSUs, outstanding, weighted average grant-date fair value, beginning balance Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Restricted stock awards and PSUs, granted, weighted average grant-date fair value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Restricted stock awards and PSUs, vested, weighted average grant-date fair value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Restricted stock awards and PSUs, forfeited, weighted average grant-date fair value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Restricted stock awards and PSUs, outstanding, weighted average grant-date fair value, ending balance Income Tax Disclosure [Abstract] Effective Income Tax Rate, Continuing Operations Effective Income Tax Rate, Continuing Operations Effective tax rate from discontinued operations Effective Tax Rate From Discontinued Operation A ratio calculated by dividing the reported amount of income tax expense attributable to discontinued operations for the period by GAAP-basis pretax income from discontinued operations. Net Income tax payments (refunds) Income Taxes Paid, Net Statutory tax rate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate Gross unrecognized tax benefits Unrecognized Tax Benefits Possible unrecognized tax benefits reduction during the next twelve months Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit Tax loss related to investment in subsidiary Tax Loss Related to Investment in Subsidiary This represents tax loss will be reported and/or disclosed related to investment in subsidiary in tax return. Tax benefit related to investment in subsidiary Tax Benefit Related to Investment in Subsidiary This represents tax benefit derived from deductible losses relating to investment in subsidiaries in tax return. Reconciliation of the denominators of the earnings per share calculations Schedule of Earnings Per Share Reconciliation [Table Text Block] Financial assets and financial liabilities measured at fair value on recurring basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Derivative Instruments and Hedging Activities Disclosure [Abstract] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Derivative Instrument Risk [Axis] Derivative Instrument Risk [Axis] Derivative Contract Type [Domain] Derivative Contract Type [Domain] Commodity [Member] Commodity [Member] Foreign exchange [Member] Foreign Exchange [Member] Other [Member] Other Contract [Member] Hedging Designation [Axis] Hedging Designation [Axis] Hedging Designation [Domain] Hedging Designation [Domain] Designated for hedge accounting [Member] Designated as Hedging Instrument [Member] Not designated for hedge accounting [Member] Not Designated as Hedging Instrument [Member] Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Derivative liabilities (accrued expenses, other payables and long-term liabilities) Statement of Other Comprehensive Income [Abstract] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] Taxes(benefit), foreign currency translation adjustment and other Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax Taxes(benefit), unrealized holding gain (loss) on derivatives Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax Taxes(benefit), reclassification for gain (loss) on derivatives included in net earnings Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, Tax Taxes(benefit), net unrealized gain (loss) on derivatives Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax Taxes(benefit), reclassification adjustment from defined benefit plan changes Other Comprehensive Income (Loss), Finalization of Pension and Non-Pension Postretirement Plan Valuation, Tax Taxes(benefit), defined benefit obligation Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Tax Income taxes Income Tax Disclosure [Text Block] Schedule of Entity-Wide Information, Revenue from External Customers by Products and Services [Table] Revenue from External Customers by Products and Services [Table] Products and Services [Axis] Products and Services [Axis] Products and Services [Domain] Products and Services [Domain] Steel products [Member] Steel Products [Member] Steel products. Industrial materials [Member] Industrial Materials [Member] Industrial materials. Nonferrous scrap [Member] Nonferrous Scrap [Member] Nonferrous scrap. Ferrous scrap [Member] Ferrous Scrap [Member] Ferrous scrap. Construction materials [Member] Construction Materials [Member] Construction materials. Nonferrous products [Member] Nonferrous Products [Member] Nonferrous products. Other [Member] Other Product [Member] Other. Entity-Wide Information, Revenue from External Customer [Line Items] Revenue from External Customer [Line Items] Net sales Sales Revenue, Goods, Net Fair value Fair Value Disclosures [Text Block] Subsequent Events [Abstract] Subsequent Events [Text Block] Subsequent Events [Text Block] Current assets Assets of Disposal Group, Including Discontinued Operation, Current Revenue Disposal Group, Including Discontinued Operation, Revenue Earnings (loss) before taxes Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax Commodity contract commitments Schedule of Derivative Instruments [Table Text Block] Derivatives not designated as hedging instruments Schedule of Other Derivatives Not Designated as Hedging Instruments, Statements of Financial Performance and Financial Position, Location [Table Text Block] Derivatives designated as fair value hedging instruments Schedule of Fair Value Hedging Instruments, Statements of Financial Performance and Financial Position, Location [Table Text Block] Hedged items designated as fair value hedging instruments Hedged Items Designated as Fair Value Hedging Instruments [Table Text Block] Tabular disclosure for the underlying items in fair value hedges of (a) the location and amount of gains and losses reported in the statements of financial performance and/or(b) the location and fair value amounts of the instruments reported in the statements of financial position. Effective portion of derivatives designated as cash flow hedging instruments recognized In accumulated other comprehensive income (loss) Schedule of Derivative Instruments, Effect on Other Comprehensive Income (Loss) [Table Text Block] Effective portion of derivatives designated as cash flow hedging instruments reclassified from accumulated other comprehensive income (loss) Schedule of Cash Flow Hedges Included in Accumulated Other Comprehensive Income (Loss) [Table Text Block] Derivative assets Schedule of Derivative Assets at Fair Value [Table Text Block] Derivative liabilities Schedule of Derivative Liabilities at Fair Value [Table Text Block] Changes in the carrying amount of goodwill Schedule of Goodwill [Table Text Block] Statement of Stockholders' Equity [Abstract] Statement, Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Common Stock Common Stock [Member] Additional Paid-In Capital Additional Paid-in Capital [Member] Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income (Loss) [Member] Retained Earnings Retained Earnings [Member] Treasury Stock Treasury Stock [Member] Noncontrolling Interests Noncontrolling Interest [Member] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Beginning balance, shares Common Stock, Shares, Issued Beginning balance, treasury stock, value Treasury Stock, Value Beginning balance, treasury stock, shares Treasury Stock, Shares Comprehensive income (loss): Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract] Net earnings Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Other comprehensive income (loss) Other Comprehensive Income (Loss), Net of Tax Comprehensive income Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Cash dividends Dividends, Common Stock, Cash Issuance of stock under incentive and purchase plans, net of forfeitures Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures Issuance of stock under incentive and purchase plans, net of forfeitures, shares Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures Share-based compensation Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition Contribution from (purchase of) noncontrolling interests Proceeds from (Payments to) Noncontrolling Interests Ending balance, treasury stock, value Ending balance, treasury stock, shares Ending balance Ending balance, shares Combined information for shares subject to options and SARs excluding the cash component Schedule of Share-based Compensation, Stock Options and Stock Appreciation Rights Award Activity [Table Text Block] Activity of restricted stock awards and PSUs excluding the cash component of PSUs Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block] Reconciliation of the denominators of the earnings per share Earnings Per Share Reconciliation [Abstract] Shares outstanding for basic earnings per share Weighted Average Number of Shares Outstanding, Basic Stock-based incentive/purchase plans Incremental Common Shares Attributable to Share-based Payment Arrangements Shares outstanding for diluted earnings per share Weighted Average Number of Shares Outstanding, Diluted Goodwill and other intangible assets Goodwill and Intangible Assets Disclosure [Text Block] Fair value measurements recognized loss [Member] Fair Value Measurements Recognized Loss [Member] It represents recogized loss (gain) incurred during the period relating to assets measured at fair value at a specified date. Fair Value, Measurements, Nonrecurring [Member] Fair Value, Measurements, Nonrecurring [Member] Plant, property and equipment Property, Plant, and Equipment, Fair Value Disclosure Impairment charges for plant, property and equipment Impairment of Long-Lived Assets to be Disposed of Fair value of long-term debt, predominantly publicly held Long-term Debt, Fair Value Number of fair value hierarchy Number of Fair Value Hierarchy This represents number of levels used to prioritize the inputs to valuation techniques used to measure fair value. The fair value hierarchy gives the highest priority to quoted prices (unadjusted) in active markets for identical assets or liabilities (Level 1), inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly (Level 2), and the lowest priority to unobservable inputs (Level 3). Where the quoted price in an active market for the identical liability is not available, the Level 1 input is the quoted price of an identical liability when traded as an asset. Restructuring and Related Activities [Abstract] Severance costs Derivative Instruments, Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk [Table] Derivative Instruments, Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk [Table] Commodity [Member] Commodity Contract [Member] Foreign exchange [Member] Foreign Exchange Contract [Member] Interest rate [Member] Interest Rate Contract [Member] Derivative Instruments, Gain (Loss) by Income Statement Location [Axis] Income Statement Location [Axis] Income Statement and Other Comprehensive Income Location [Domain] Income Statement Location [Domain] Cost of goods sold [Member] Cost of Sales [Member] Net sales [Member] Sales [Member] SG&A expenses [Member] Operating Expense [Member] Interest expense [Member] Interest Expense [Member] Derivative Instruments, Gain (Loss) [Line Items] Derivative Instruments, Gain (Loss) [Line Items] Gain (loss), net of taxes for cash flow hedges reclassified from AOCI Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net Inventory Disclosure [Abstract] Inventory, LIFO reserve Inventory, LIFO Reserve Percentage of total inventory valued at LIFO Percentage of LIFO Inventory Raw materials Inventory, Raw Materials, Gross Effect of LIFO Inventory Liquidation on Income Effect of LIFO Inventory Liquidation on Income Share-based compensation Disclosure of Compensation Related Costs, Share-based Payments [Text Block] SG&A expenses [Member] Gain (loss) before taxes for derivatives not designated as hedges Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net Organization, Consolidation and Presentation of Financial Statements [Abstract] Dispositions Acquisitions And Dispositions [Text Block] Business acquisitions (or series of individually immaterial business acquisitions) completed during the period and planned or completed dispositions. This element may include fixed asset sales and plant closings. Transfers and Servicing [Abstract] Sales of accounts receivable Transfers and Servicing of Financial Assets [Text Block] Inventories Inventory Disclosure [Text Block] Schedule of Revenues from External Customers and Long-Lived Assets [Table] Schedule of Revenues from External Customers and Long-Lived Assets [Table] Geographical [Axis] Geographical [Axis] Segment, Geographical [Domain] Segment, Geographical [Domain] United States [Member] UNITED STATES Europe [Member] Segment, Geographical, Groups of Countries, Group One [Member] Asia [Member] Segment, Geographical, Groups of Countries, Group Two [Member] Australia [Member] Segment Geographical Groups Of Countries Group Three [Member] Segment Geographical Groups Of Countries Group Three Member. Other [Member] Other Foreign Countries [Member] Other Foreign Countries Member Revenues from External Customers and Long-Lived Assets [Line Items] Revenues from External Customers and Long-Lived Assets [Line Items] Gain (loss) before taxes for hedged items of fair value hedges Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge Gain (loss) before taxes for fair value hedges Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments Commitments and Contingencies Disclosure [Abstract] Commitments And contingencies Commitments and Contingencies Disclosure [Text Block] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Segment, Continuing Operations [Member] Segment, Continuing Operations [Member] Corporate [Member] Corporate [Member] Eliminations [Member] Intersegment Elimination [Member] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Net sales-unaffiliated customers Intersegment sales Segment Reporting Information, Intersegment Revenue Net sales Segment Reporting Information, Revenue for Reportable Segment Adjusted operating profit (loss) Adjusted Operating Profit Loss from Continuing Operation It represents non-GAAP financial measures of adjusted operating profit (loss) from continuing operations. Total assets Assets exclude discontinued operations It represents amount of assets excluding assets from discontinued operations. Earnings from continuing operations Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest Income taxes (benefit) Income Tax Expense (Benefit) Interest expense Interest Expense Discounts on sales of accounts receivable Gain (Loss) on Securitization of Financial Assets Adjusted operating profit from continuing operations Adjusted operating profit (loss) from discontinued operations Adjusted operating profit (loss) from discontinued operations It represents non-GAAP financial measures of adjusted operating profit (loss) from discontinued operations. Adjusted operating profit Adjusted Segment Reporting Operating Profit Loss It represents non-GAAP financial measures of adjusted segment reporting operating profit (loss). Statement of Financial Position [Abstract] Allowance for doubtful accounts Allowance for Doubtful Accounts Receivable, Current Common stock, par value Common Stock, Par or Stated Value Per Share Common stock, shares authorized Common Stock, Shares Authorized Common stock, shares issued Common stock, shares outstanding Common Stock, Shares, Outstanding Treasury stock, shares Business segments Segment Reporting Disclosure [Text Block] Gross carrying amounts of the Company's intangible assets Finite-Lived Intangible Assets, Gross Amortization expense for intangible assets Amortization of Intangible Assets Statement of Cash Flows [Abstract] Cash flows from (used by) operating activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Adjustments to reconcile net earnings to cash flows from (used by) operating activities: Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation and amortization Depreciation, Depletion and Amortization Provision for losses on receivables, net Provision for Doubtful Accounts Share-based compensation Share-based Compensation Amortization of interest rate swaps termination gain Amortization of Deferred Hedge Gains Deferred income taxes (benefit) Deferred Income Taxes and Tax Credits Net (gain) loss on sale of cost method investment and other Gain (Loss) on Sale of Property Plant Equipment Write-down of inventory Inventory Write-down Asset impairment Asset Impairment Charges Changes in operating assets and liabilities, net of acquisitions: Increase (Decrease) in Operating Capital [Abstract] Decrease in accounts receivable Increase (Decrease) in Accounts Receivable Accounts receivable sold (repurchased), net Increase Decrease in Accounts Receivable Sold Repurchased It represents amount of net change in receivables sold (repurchased). Increase in inventories Increase (Decrease) in Inventories Decrease (increase) in other assets Increase (Decrease) in Other Operating Assets Decrease in accounts payable, accrued expenses, other payables and income taxes Increase (Decrease) in Accounts Payable and Accrued Liabilities Increase (decrease) in other long-term liabilities Increase (Decrease) in Other Noncurrent Liabilities Net cash flows from (used by) operating activities Net Cash Provided by (Used in) Operating Activities Cash flows from (used by) investing activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Capital expenditures Payments to Acquire Property, Plant, and Equipment Proceeds from the sale of property, plant and equipment and other Proceeds from Sale of Property, Plant, and Equipment Proceeds from the sale of cost method investment Proceeds from Sale of Equity Method Investments Increase in deposit for letters of credit Increase Decrease In Deposit For Letters Of Credit It represents cash outflow (inflow) due to increase (Decrease) in deposit for letters of credit. Net cash flows from (used by) investing activities Net Cash Provided by (Used in) Investing Activities Cash flows from (used by) financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Increase in documentary letters of credit Increase Decrease in Documentary Letters of Credit It represents cash inflow (outflow) due to increase (decrease) in documentary letter of credit. Short-term borrowings, net change Proceeds from (Repayments of) Short-term Debt Repayments on long-term debt Repayments of Long-term Debt Stock issued under incentive and purchase plans, net of forfeitures Proceeds from Issuance of Shares under Incentive and Share-based Compensation Plans, Including Stock Options Cash dividends Payments of Ordinary Dividends, Common Stock Net cash flows from (used by) financing activities Net Cash Provided by (Used in) Financing Activities Effect of exchange rate changes on cash Effect of Exchange Rate on Cash and Cash Equivalents Increase in cash and cash equivalents Cash and Cash Equivalents, Period Increase (Decrease) Cash and cash equivalents at beginning of year Cash, Cash Equivalents, and Short-term Investments Cash and cash equivalents at end of period Severance Restructuring and Related Activities Disclosure [Text Block] Debt Disclosure [Abstract] Debt Instrument [Table] Schedule of Long-term Debt Instruments [Table] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] 5.625% notes due November 2013 [Member] Five Point Six Two Five Percent Notes Due November2013 [Member] Five Point Six Two Five Percent Notes Due November 2013. 6.50% notes due July 2017 [Member] Six Point Five Zero Percent Notes Due July2017 [Member] Six Point Five Zero Percent Notes Due July 2017. 7.35% notes due August 2018 [Member] Seven Point Three Five Percent Notes Due August2018 [Member] Seven point three five percent notes due august 2018. Other, including equipment notes [Member] Other Including Equipment Notes [Member] Other Including Equipment Notes. Debt Instrument [Line Items] Debt Instrument [Line Items] Debt instrument, face amount Debt Instrument, Face Amount Debt instrument, interest rate, stated percentage Debt Instrument, Interest Rate, Stated Percentage Debt instrument, maturity date Debt Instrument, Maturity Date, Description Weighted average interest rate Long-term Debt, Weighted Average Interest Rate Total long-term debt including current maturities Debt and Capital Lease Obligations Current maturities of long-term debt Long-term Debt and Capital Lease Obligations, Current Long-term debt Long-term Debt and Capital Lease Obligations Gain, (loss), net of taxes for cash flow hedges recognized in AOCI Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net Income Statement [Abstract] Costs and expenses: Costs and Expenses [Abstract] Cost of goods sold Cost of Goods Sold Selling, general and administrative expenses Selling, General and Administrative Expense Interest expense Total costs and expenses Costs and Expenses Earnings from continuing operations before taxes Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest Earnings (loss) from discontinued operations before taxes Income taxes (benefit) Discontinued Operation, Tax Effect of Discontinued Operation Earnings (loss) from discontinued operations Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest Net earnings Less net earnings attributable to noncontrolling interests Net Income (Loss) Attributable to Noncontrolling Interest Net earnings attributable to CMC Net Income (Loss) Attributable to Parent Basic earnings (loss) per share attributable to CMC: Earnings Per Share, Basic [Abstract] Earnings from continuing operations Income (Loss) from Continuing Operations, Per Basic Share Earnings (loss) from discontinued operations Income (Loss) from Discontinued Operations, Net of Tax, Per Basic Share Net earnings Earnings Per Share, Basic Diluted earnings (loss) per share attributable to CMC: Earnings Per Share, Diluted [Abstract] Earnings from continuing operations Income (Loss) from Continuing Operations, Per Diluted Share Earnings (loss) from discontinued operations Income (Loss) from Discontinued Operations, Net of Tax, Per Diluted Share Net earnings Earnings Per Share, Diluted Cash dividends per share Common Stock, Dividends, Per Share, Cash Paid Average basic shares outstanding Average diluted shares outstanding Derivative [Table] Derivative [Table] Derivative, by Nature [Axis] Derivative, by Nature [Axis] Derivative, Name [Domain] Derivative, Name [Domain] Aluminum [Member] Aluminum [Member] Aluminum. Copper [Member] Copper [Member] Copper. Natural Gas [Member] Natural Gas [Member] Long [Member] Long [Member] Long position. Short [Member] Short [Member] Short position. Derivative [Line Items] Derivative [Line Items] Commodity Contract Commitments Commodity Contract Commitments This represents quantities specified in agreements to purchase or sell commodity resources at some future point held at each balance sheet date. Energy Contract Commitments Energy Contract Commitment This represents quantities specified in agreements to purchase or sell energy resources at some future point held at each balance sheet date. Summary of certain financial information from continuing operations by reportable segment Schedule of Segment Reporting Information, by Segment [Table Text Block] Reconciliation of consolidated adjusted operating profit (loss) to earnings (loss) from continuing operations Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Table Text Block] External net sales from continuing operations by major product and geographic area and long-lived assets by geographic area Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas [Table Text Block] Derivatives and risk management Derivative Instruments and Hedging Activities Disclosure [Text Block] Long-term debt, including the net effect of the deferred gain from the termination of the interest rate swaps Schedule of Long-term Debt Instruments [Table Text Block] Schedule of Securitization or Asset-backed Financing Arrangements, Financial Asset for which Transfer is Accounted as Sale [Table] Schedule of Securitization or Asset-backed Financing Arrangements, Financial Asset for which Transfer is Accounted as Sale [Table] Domestic Sale Of Accounts Receivable [Member] Domestic Country Sale Of Accounts Receivable [Member] Domestic country sale of accounts receivable. International [Member] International [Member] International. Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items] Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items] Number of financial institutions Number of financial institutions It represents number of financial institutions mentioned in current filing. Maximum advance limit for receivables sold Sale of Receivables Maximum Facility It represents maximum amount of advance that can be received from financial institutions for all accounts receivables sold under the agreement. Accounts receivable sold Accounts Receivable Sold It represents amount of accounts receivables sold to a third party. Advance payment received on sale of account receivable Advance Payment Received on Sale of Account Receivable It represents actual amount of advance payment received on accounts receivable sold. Outstanding deferred purchase price of receivables sold Outstanding Deferred Purchase Price of Receivables Sold It represents amount of outstanding deferred purchase price until ultimate collection of the underlying receivables sold. Proceed from sales of receivables Proceeds from Sale and Collection of Receivables Cash payment to owners of receivables Payments to Acquire Receivables Discount on domestic and international sales of accounts receivables Revolving credit facility [Member] Revolving Credit Facility [Member] Letter of Credit [Member] Letter of Credit [Member] CMCZ [Member] Cmcz [Member] Cmcz. Line of credit facility, current borrowing capacity Line of Credit Facility, Current Borrowing Capacity Revolving credit facility, maturity date Line of Credit Facility, Expiration Date Revolving credit facility, maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Stand by letters of credit outstanding amount Stand by letters of credit outstanding amount The total amount of the contingent obligation under stand-by letters of credit outstanding as of the reporting date. Minimum interest coverage ratio Minimum Interest Coverage Ratio This represents minimum interest coverage ratio applicable to current period stated in debt covenant. Actual interest coverage ratio Interest Coverage Ratio This represents the actual interest Coverage Ratio for applicable date. Maximum debt to capitalization ratio Maximum Debt to Capitalization Ratio It represents maximum debt to capitalization ratio stated in the debt covenant. Actual debt to capitalization ratio Debt to Capitalization Ratio It represents actual debt to capitalization ratio for an applicable date. Net proceeds from termination of interest rate swaps Net Proceeds From Termination Of Interest Rate Swaps It represents net cash inflow provided by termination of interest rate swap agreements. Deferred gain on termination of interest rate swaps Deferred Gain (Loss) on Discontinuation of Interest Rate Fair Value Hedge Amortization of deferred gain from termination of interest rate fair value hedge Gain (Loss) on Fair Value Hedges Recognized in Earnings Line of credit facility, amount outstanding Line of Credit Facility, Amount Outstanding Short-term debt weighted average interest rate Short-term Debt, Weighted Average Interest Rate Interest costs capitalized Interest Costs Capitalized Interest paid Interest Paid Financial information for discontinued operations Schedule of Disposal Groups, Including Discontinued Operations, Income Statement, Balance Sheet and Additional Disclosures [Table Text Block] Assets Assets [Abstract] Current assets: Assets, Current [Abstract] Cash and cash equivalents Accounts receivable (less allowance for doubtful accounts of $9,998 and $9,480) Accounts Receivable, Net, Current Inventories, net Inventory, Net Other Other Assets, Current Total current assets Assets, Current Property, plant and equipment: Property, Plant and Equipment [Abstract] Land Land Buildings and improvements Buildings and Improvements, Gross Equipment Machinery and Equipment, Gross Construction in process Construction in Progress, Gross Property, plant and equipment, Gross Property, Plant and Equipment, Gross Less accumulated depreciation and amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Property, plant and equipment, Net Property, Plant and Equipment, Net Goodwill Other assets Other Assets, Noncurrent Total assets Assets Liabilities and stockholders’ equity Liabilities and Equity [Abstract] Current liabilities: Liabilities, Current [Abstract] Accounts payable-trade Accounts Payable, Trade, Current Accounts payable-documentary letters of credit Accounts Payable Documentary Letters of Credit It represents accounts payable documentary letters of credit. Accrued expenses and other payables Accrued Liabilities, Current Notes payable Short-term Bank Loans and Notes Payable Total current liabilities Liabilities, Current Deferred income taxes Deferred Tax Liabilities, Net, Noncurrent Other long-term liabilities Other Liabilities, Noncurrent Long-term debt Total liabilities Liabilities Commitments and contingencies Commitments and Contingencies Stockholders’ equity: Stockholders' Equity Attributable to Parent [Abstract] Common stock, par value $0.01 per share; authorized 200,000,000 shares; issued 129,060,664 shares; outstanding 116,448,898 and 116,351,424 shares Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital, Common Stock Accumulated other comprehensive income (loss) Accumulated Other Comprehensive Income (Loss), Net of Tax Retained earnings Retained Earnings (Accumulated Deficit) Less treasury stock, 12,611,766 and 12,709,240 shares at cost Stockholders’ equity attributable to CMC Stockholders' Equity Attributable to Parent Stockholders’ equity attributable to noncontrolling interests Stockholders' Equity Attributable to Noncontrolling Interest Total equity Total liabilities and stockholders’ equity Liabilities and Equity Number of antidilutive securities excluded from computation of diluted earnings per share Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Treasury Stock, Shares, Acquired Treasury Stock, Shares, Acquired Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased Trinecke Zelezarny [Member] Trinecke Zelezarny [Member] Trinecke Zelezarny, a Czech Republic joint-stock company. Joist And Deck Operations [Member] Joist And Deck Operations [Member] Joist and deck operations. Percentage of Ownership before Transaction Sale of Stock, Percentage of Ownership before Transaction Cost-method Investments, Realized Gains Cost-method Investments, Realized Gains Number of properties sold Number of Properties Sold During Period It represents number of real properties sold during period. Current interest rate [Member] Current Interest Rate [Member] Current Interest Rate [Member] Long-term interest rate [Member] Long Term Interest Rate [Member] Long term interest rate. Derivative assets (other current assets and other assets) Net earnings Other comprehensive income (loss), net of taxes: Other Comprehensive Income (Loss), Net of Tax [Abstract] Foreign currency translation adjustment and other, net of taxes (benefit) of $11,792 and $(40,667) Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Net unrealized gain (loss) on derivatives: Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax [Abstract] Unrealized holding gain (loss), net of taxes of $88 and $324 Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax Less: Reclassification for gain (loss) included in net earnings, net of taxes of $49 and $164 Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, Net of Tax Net unrealized gain (loss) on derivatives, net of taxes of $39 and $160 Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax Defined benefit obligation: Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax [Abstract] Amortization of prior service cost, net of taxes (benefit) Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost Recognized in Net Periodic Pension Cost, Net of Tax Adjustment from plan changes, net of taxes (benefit) of $308 and $0 Other Comprehensive Income (Loss), Finalization of Pension and Non-Pension Postretirement Plan Valuation, Net of Tax Defined benefit obligation, net of taxes (benefit) of $308 and $0 Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax Other comprehensive income (loss) Comprehensive income PSUs [Member] PSUs [Member] Performance stock units. Share Based Liability Awards [Member] Phantom Share Units (PSUs) [Member] Share-based compensation expense Allocated Share-based Compensation Expense Unrecognized pre-tax compensation cost Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized Period of unrecognized pre-tax compensation to be recognized Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition Shares available for future grants Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Vesting period in years Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Equivalent number of shares granted Equivalent number of shares outstanding Equivalent number of shares expected to vest Share-based compensation arrangement by share-based payment award, equivalent shares expected to vest Equivalent number of shares expected to vest under share-based compensation arrangement as of the balance sheet date. Accounting Policies [Abstract] Accounting policies Significant Accounting Policies [Text Block] Loss Contingencies [Table] Loss Contingencies [Table] Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Class Action Antitrust Lawsuit [Member] Class Action Antitrust Lawsuit [Member] Class Action Antitrust Lawsuit [Member] Guarantor Obligations, Nature [Axis] Guarantor Obligations, Nature [Axis] Guarantor Obligations, Nature [Domain] Guarantor Obligations, Nature [Domain] Guarantee of Indebtedness of Others [Member] Guarantee of Indebtedness of Others [Member] Loss Contingencies [Line Items] Loss Contingencies [Line Items] Number of steel manufacturing companies Number of steel manufacturing companies This represents number of steel manufacturing companies mentioned in current filing. Number of States Number of States This represnts number of states or provinces mentioned in current filing. Maximum credit facility Guarantor obligations, maximum exposure Guarantor Obligations, Maximum Exposure, Undiscounted Accounting principles Basis of Accounting, Policy [Policy Text Block] Recent accounting pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Notional value of foreign currency contract commitments Notional Amount of Foreign Currency Derivatives Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] Options and SARs excluding cash components [Member] Options and SARs excluding cash component [Member] Options and SARs excluding cash component [Member] Options and SARs, outstanding, number, beginning balance Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Options and SARs, granted, number Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Options and SARs, forfeited / expired, number Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period Options and SARs, outstanding, number, ending balance Options and SARs, exercisable, number Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Options and SARs, outstanding, weighted average exercise price, beginning balance Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Options and SARs, granted, weighted average exercise price Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Options and SARs, forfeited / expired, weighted average exercise price Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price Options and SARs, outstanding, weighted average exercise price, ending balance Options and SARs, exercisable, weighted average exercise price Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price Options and SARs, outstanding, weighted average remaining contractual life (years) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Options and SARs, exercisable, weighted average remaining contractual life (years) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Options and SARs, outstanding, aggregated intrinsic value Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value Options and SARs, exercisable, aggregated intrinsic value Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Credit Arrangements Debt Disclosure [Text Block] Document And Entity Information [Abstract] -- None. No documentation exists for this element. -- Entities [Table] Entities [Table] Entity Information [Line Items] Entity Information [Line Items] Trading Symbol Trading Symbol Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Document Type Document Type Document Period End Date Document Period End Date Amendment Flag Amendment Flag Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Current Fiscal Year End Date Current Fiscal Year End Date Entity Tax Identification Number Entity Tax Identification Number Entity Filer Category Entity Filer Category Entity Current Reporting Status Entity Current Reporting Status Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding