It represents actual debt to capitalization ratio for an applicable date.

No definition available.

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Namespace Prefix:	cmc_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

It represents actual interest coverage ratio for an applicable date.

+ References

No definition available.

+ Details

Name:	cmc_InterestCoverageRatio
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Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

It represents maximum debt to capitalization ratio stated in the debt covenant.

+ References

No definition available.

+ Details

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Namespace Prefix:	cmc_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

This represents minimum interest coverage ratio applicable to current period stated in debt covenant.

+ References

No definition available.

+ Details

Name:	cmc_MinimumInterestCoverageRatio
Namespace Prefix:	cmc_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

It represents minimum liquidity that the Company is required to maintain under the contractual terms.

+ References

No definition available.

+ Details

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Namespace Prefix:	cmc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

It represents net cash inflow provided by termination of interest rate swap agreements.

+ References

No definition available.

+ Details

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

- Definition

It represents percentage of purchase price in relation to principal amount in case of debt redemption.

+ References

No definition available.

+ Details

Name:	cmc_RedemptionPurchasePriceToPrincipalAmountPercentage
Namespace Prefix:	cmc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of expense charged against earnings by an Entity to record deferred gains and losses on hedge instruments. Examples include gain on economic hedges, amortization of gain on designated fair value hedge and so forth.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.3)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=34725769&loc=d3e28878-108400

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

+ Details

Name:	us-gaap_DebtInstrumentInterestRateEffectivePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Description of the maturity date of the debt instrument including whether the debt matures serially and, if so, a brief description of the serial maturities.

+ References

+ Details

Name:	us-gaap_DebtInstrumentMaturityDateDescription
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount as of the balance sheet date of the unamortized adjustment to the carrying value of an interest-bearing hedged item made under an effective interest rate fair value hedge that is amortized upon discontinuation of the interest rate fair value hedge.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 25

-Section 35

-Paragraph 9

-URI http://asc.fasb.org/extlink&oid=6439857&loc=d3e75592-113984

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of cash paid for interest during the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4297-108586

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 25

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3536-108585

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of the total principal payments made during the annual reporting period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21475-112644

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

Name:	us-gaap_LineOfCreditFacilityAnnualPrincipalPayment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Average amount borrowed under the credit facility during the period.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityAverageOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Date the credit facility terminates, in CCYY-MM-DD format.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityExpirationDate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value of the amount outstanding under the credit facility.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13433-108611

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-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13476-108611

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	dei_LegalEntityAxis=cmc_CmcpMember
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- Details

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CREDIT ARRANGEMENTS (Narrative) (Details)		3 Months Ended		9 Months Ended		12 Months Ended
CREDIT ARRANGEMENTS (Narrative) (Details)	Jun. 26, 2014 USD ($)	May. 31, 2015 USD ($)	May. 31, 2014 USD ($)	May. 31, 2015 USD ($)	May. 31, 2014 USD ($)	Aug. 31, 2014 USD ($)	Aug. 31, 2012 USD ($)	May. 31, 2013 USD ($)	Aug. 31, 2008 USD ($)	Jul. 31, 2007 USD ($)
Debt Instrument [Line Items]
Net proceeds from termination of interest rate swaps							$ 52,700,000
Unamortized deferred gain on termination of interest rate swaps		$ 21,100,000		$ 21,100,000		$ 26,800,000
Amortization of interest rate swaps termination gain		1,900,000	$ 1,900,000	5,698,000	$ 5,698,000
Interest paid		10,600,000	$ 9,600,000	53,500,000	$ 51,900,000
CMCP
Debt Instrument [Line Items]
Revolving credit facility current borrowing capacity		57,500,000.0		57,500,000.0
Total borrowing				49,600,000
Total payments				49,600,000
$330 million notes at 4.875% due May 2023
Debt Instrument [Line Items]
Debt instrument, face amount		$ 330,000,000		$ 330,000,000		$ 330,000,000		$ 330,000,000
Debt instrument, interest rate, stated percentage		4.875%		4.875%		4.875%		4.875%
Debt instrument, maturity date				May 15, 2023		May 15, 2023
Redemption purchase price to principal amount, percentage								100.00%
Change of control triggering event
Debt Instrument [Line Items]
Redemption purchase price to principal amount, percentage								101.00%
$500 million notes at 7.35% due August 2018
Debt Instrument [Line Items]
Debt instrument, face amount		$ 500,000,000		$ 500,000,000		$ 500,000,000			$ 500,000,000
Debt instrument, interest rate, stated percentage		7.35%		7.35%		7.35%			7.35%
Debt instrument, maturity date				August 2018		August 2018
Debt instrument, effective interest rate									6.40%
$400 million notes at 6.50% due July 2017
Debt Instrument [Line Items]
Debt instrument, face amount		$ 400,000,000		$ 400,000,000		$ 400,000,000				$ 400,000,000
Debt instrument, interest rate, stated percentage		6.50%		6.50%		6.50%				6.50%
Debt instrument, maturity date				July 2017		July 2017
Debt instrument, effective interest rate										5.74%
Revolving credit facility
Debt Instrument [Line Items]
Revolving credit facility current borrowing capacity	$ 350,000,000
Revolving credit facility, maturity date				Jun. 26, 2019
Revolving credit facility, maximum borrowing capacity	$ 500,000,000
Minimum interest coverage ratio	2.50
Maximum debt to capitalization ratio	0.60
Minimum liquidity required	$ 150,000,000
Actual interest coverage ratio		6.26		6.26
Actual debt to capitalization ratio		0.48		0.48
Revolving credit facility, amount drawn		$ 0		$ 0		$ 0
Stand-by letters of credit
Debt Instrument [Line Items]
Revolving credit facility current borrowing capacity	$ 50,000,000
Stand by letters of credit outstanding amount		$ 23,400,000		$ 23,400,000		$ 28,100,000