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Debt - Private Placement Shelf Agreement (Details) (Maximum, Senior Notes, Private Placement Shelf Agreement, USD $)
In Thousands, unless otherwise specified
Sep. 22, 2014
Maximum | Senior Notes | Private Placement Shelf Agreement
  
Debt Instrument [Line Items]  
Agreement face amount $ 100,000graybar_DebtInstrumentAgreementFaceAmount
/ us-gaap_DebtInstrumentAxis
= graybar_PrivatePlacementShelfAgreementMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember