Line of Credit Facility, Accordion Feature, Increase Limit

No definition available.

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Namespace Prefix:	graybar_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Private Placement Issuance Period

+ References

No definition available.

+ Details

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Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
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+ Details

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

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
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

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

- Definition

Amount of the cost of borrowed funds accounted for as interest expense.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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+ Details

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

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

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

- Definition

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

+ References

+ Details

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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

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
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

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

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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

- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

+ References

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+ Details

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Balance Type:	credit
Period Type:	instant

- Details

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- Details

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- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=graybar_PrudentialPrivatePlacementShelfAgreementMember
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Data Type:	na
Balance Type:
Period Type:

- Details

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Data Type:	na
Balance Type:
Period Type:

- Details

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Data Type:	na
Balance Type:
Period Type:

- Details

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Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Data Type:	na
Balance Type:
Period Type:

- Details

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Balance Type:
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- Details

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- Details

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Debt (Narrative) (Details) - USD ($)		3 Months Ended
Debt (Narrative) (Details) - USD ($)	Aug. 10, 2018	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Line of Credit Facility [Line Items]
Remaining borrowing capacity		$ 479,500,000		$ 611,500,000
Credit agreement commitment fee percentage		0.40%
Short-term borrowings		$ 270,000,000.0		138,000,000.0
Interest expense, net		900,000	$ 1,800,000
Letters of credit outstanding		5,600,000		5,600,000
Minimum
Line of Credit Facility [Line Items]
Short-term borrowings		55,000,000.0	120,000,000.0
Maximum
Line of Credit Facility [Line Items]
Short-term borrowings		270,000,000.0	$ 250,000,000.0
Revolving Credit Facility
Line of Credit Facility [Line Items]
Short-term borrowings		270,000,000.0		138,000,000.0
Amended Credit Agreement
Line of Credit Facility [Line Items]
Letters of credit outstanding		500,000		$ 500,000
Prudential Private Placement Shelf Agreement
Line of Credit Facility [Line Items]
Agreement face amount		$ 100,000,000.0
Issuance period		3 years
MetLife Private Placement Shelf Agreement
Line of Credit Facility [Line Items]
Agreement face amount		$ 100,000,000.0
Issuance period		3 years
Prudential Shelf Agreement Or MetLife Shelf Agreement [Member]
Line of Credit Facility [Line Items]
Notes issued face amount		$ 0
Line of credit \| Amended Credit Agreement \| Revolving Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 750,000,000.0
Accordian feature, increase limit		$ 375,000,000.0
Expiration date		Aug. 10, 2023
Debt instrument, term	5 years
Line of credit \| Amended Credit Agreement \| Letter of Credit Sub-Facility [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 25,000,000.0
Line of credit \| Amended Credit Agreement \| Bridge Loan \| Graybar Canada [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity		100,000,000.0
Line of credit \| Amended Credit Agreement \| Bridge Loan \| UNITED STATES
Line of Credit Facility [Line Items]
Maximum borrowing capacity		75,000,000.0
Line of credit \| Amended Credit Agreement \| Bridge Loan \| CANADA
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 20,000,000.0