Debt instrument installment due frequency term.

No definition available.

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Namespace Prefix:	kop_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument number of repayment installments.

+ References

No definition available.

+ Details

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Namespace Prefix:	kop_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Debt instrument offering price percentage.

+ References

No definition available.

+ Details

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Namespace Prefix:	kop_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument, offering value.

+ References

No definition available.

+ Details

Name:	kop_DebtInstrumentOfferingValue
Namespace Prefix:	kop_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Debt instrument payment commencement period.

+ References

No definition available.

+ Details

Name:	kop_DebtInstrumentPaymentCommencementPeriod
Namespace Prefix:	kop_
Data Type:	xbrli:gYearMonthItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents the carrying value of a short-term real estate loan to finance building costs. The funds are disbursed as needed or in accordance with a prearranged plan; generally, a portion of the funds is disbursed at inception and the remainder as construction progresses. The money is repaid on completion of the project, usually from the proceeds of a mortgage loan. The rate is normally higher than the prime rate, and there is usually an origination fee. The effective yield on these loans tends to be high, and the lender has a security interest in the real property. Note that there are separate concepts for the current and noncurrent portions of long-term construction loans.

+ 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 210.5-02.19(a)(1))

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

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 20

-Article 5

+ Details

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

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
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

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

- Definition

Description of the frequency of periodic payments (monthly, quarterly, annual).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 470

-Section 50

-Paragraph 3

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823

Reference 2: 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)

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

+ Details

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

- 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

+ Details

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

- Definition

Date the debt instrument was issued, in CCYY-MM-DD format.

+ References

+ Details

Name:	us-gaap_DebtInstrumentIssuanceDate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- 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

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

+ Details

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

- Definition

Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

+ References

+ Details

Name:	us-gaap_DebtInstrumentRedemptionPricePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of unused borrowing capacity under the long-term financing arrangement that is available to the entity as of the balance sheet date.

+ References

+ Details

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

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

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

- 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

The maximum amount of borrowing capacity under a line of credit that is available as of the balance sheet date for a specific purpose other than for financing goods acquired for inventory or imminent delivery to a customer.

+ References

No definition available.

+ Details

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

- 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

Name:	us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
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

The effective interest rate during the reporting period.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityInterestRateDuringPeriod
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- 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

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

- Definition

Amount of the required periodic payment applied to principal.

+ References

+ Details

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

- Definition

The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

+ References

No definition available.

+ Details

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

- Definition

Percentage of subsidiary's or equity method investee's stock owned by parent immediately after all stock transactions.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	dei_LegalEntityAxis=kop_KoppersCarbonAndChemicalCompanyLimitedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SeniorNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=kop_SeniorSecuredCreditFacilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=kop_CommittedLoanFacilityAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_ConstructionLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=kop_ThirdPartyDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=kop_LenderMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_OtherCommitmentsAxis=kop_CommittedCreditFacilityMember
Namespace Prefix:
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Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=kop_SevenPointEightSevenFivePercentSeniorNotesDueTwoThousandNineteenMember
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Debt - Additional Information (Detail) ¥ in Millions				6 Months Ended
Debt - Additional Information (Detail) ¥ in Millions	Aug. 15, 2014 USD ($)	Nov. 18, 2013 USD ($) Installment	Dec. 01, 2009 USD ($)	Jun. 30, 2015 USD ($)	Nov. 18, 2013 CNY (¥) Installment
Koppers Carbon and Chemical Company Limited [Member]
Debt Instrument [Line Items]
Percentage of owned subsidiary				60.00%
Senior Notes [Member]
Debt Instrument [Line Items]
Percentage of owned subsidiary			100.00%
Debt instrument, face amount			$ 300,000,000
Senior Secured Credit Facilities [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Revolving credit facility	$ 350,000,000
Revolving credit facility, current borrowing capacity	500,000,000
Senior secured term loan for acquiring Osmose	$ 300,000,000
Revolving credit facility, borrowing maturity date	Aug. 15, 2019
Initial interest rate	3.25%
Quarterly principal repayment obligations, interest rate	2.50%
Quarterly principal repayment obligations	$ 7,500,000
Debt instrument, unused borrowing capacity				$ 80,200,000
Letters of credit, amount outstanding				$ 61,600,000
Debt, Weighted Average Interest Rate				3.75%
Committed Loan Facility Agreements [Member] \| Construction Loans [Member]
Debt Instrument [Line Items]
Percentage of non-controlling shareholders		25.00%			25.00%
Debt maturity date		Nov. 18, 2018
Number of installments for repayment of loans \| Installment		6			6
Installment frequency for repayment of loans		6 months
Commencement period of debt repayment		2016-05
Debt, Weighted Average Interest Rate				5.81%
Committed Loan Facility Agreements [Member] \| Construction Loans [Member] \| Third Party Debt [Member]
Debt Instrument [Line Items]
Construction loan facility borrowing capacity \| ¥					¥ 198.8
Committed Loan Facility Agreements [Member] \| Construction Loans [Member] \| Lender [Member] \| Committed Credit Facility [Member]
Debt Instrument [Line Items]
Construction loan facility borrowing capacity \| ¥					66.2
Committed Loan Facility Agreements [Member] \| Construction Loans [Member] \| Koppers Carbon and Chemical Company Limited [Member]
Debt Instrument [Line Items]
Percentage of owned subsidiary		75.00%
Construction loan facility borrowing capacity		$ 44,000,000			¥ 265.0
7 7/8 Percent Senior Notes Due 2019 [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate				7.875%
Debt instrument, issuance date				Dec. 01, 2009
Debt instrument, offering price percentage			98.311%
Debt instrument, offering value			$ 294,900,000
Debt instrument, face amount			$ 300,000,000
Debt instrument, effective interest rate				8.125%
Debt instrument, redemption price percentage				103.938%
Frequency of interest payment on senior notes				Interest on the Senior Notes is payable semiannually on December 1 and June 1 each year