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Data Type:	xbrli:monetaryItemType
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The date when the principal portion of the notes is due to the holders.

No definition available.

Name:	cost_DebtInstrumentDatePrincipalDue
Namespace Prefix:	cost_
Data Type:	xbrli:gYearMonthItemType
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Period Type:	duration

- Details

Name:	cost_DebtLineItems
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The gross amount of value received by the entity resulting from the issuance of its convertible subordinated notes.

No definition available.

Name:	cost_GrossProceedsToCompany
Namespace Prefix:	cost_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

The redemption price, as a percentage of the principal amount, that the Company, upon certain events defined by the terms of the outstanding notes, will be required to make a purchase offer to redeem notes outstanding.

No definition available.

Name:	cost_RedemptionPriceCertainEvents
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Data Type:	num:percentItemType
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Period Type:	instant

The redemption price, as a percentage of the principal amount, that the Company, at its option, may redeem notes outstanding.

No definition available.

Name:	cost_RedemptionPriceCompanyOption
Namespace Prefix:	cost_
Data Type:	num:percentItemType
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Period Type:	instant

The rate of return anticipated on a bond if it is held until the maturity date.

No definition available.

Name:	cost_YieldToMaturityPercentage
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The percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

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Data Type:	num:percentItemType
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The price per share of the conversion feature embedded in the debt instrument.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 20

-Section 50

-Paragraph 5

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6928298&loc=SL6031898-161870

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-Publisher FASB

-Name FASB Staff Position (FSP)

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-Paragraph 32

-Subparagraph b

-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.

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The number of equity instruments that the holder of the debt instrument would receive if the debt was converted to equity.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 6

-Subparagraph (b)

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-Publisher FASB

-Name Accounting Standards Codification

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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 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-Paragraph 4

-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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 7: 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)(5))

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

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The stated principal amount of the debt instrument at time of issuance, which may vary from the carrying amount because of unamortized premium or discount.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

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-Name Accounting Standards Codification

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-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 21

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

The amount of debt discount that was originally recognized at the issuance of the instrument that has yet to be amortized.

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

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 21

-Paragraph 16, 20

-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.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

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-Paragraph 1A

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-Publisher FASB

-Name FASB Staff Position (FSP)

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-Name Accounting Standards Codification

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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.

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 210.5-02.19(b),22(b))

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

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

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The effective interest rate during the reporting period.

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The interest rate applicable to the portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a set, unchanging rate.