Credit Agreement (Details) (USD $)	12 Months Ended		0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Jun. 06, 2014
Line of Credit Facility [Line Items]
Fixed rate debt carrying amount in excess of fair value	$ 1,331,000	$ 323,000
Remaining borrowing capacity	483,658,000	416,847,000
Credit agreement commitment fee percentage	0.40%	0.35%
Line of credit | Credit Agreement | Revolving Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity		500,000,000	550,000,000
Accordion feature, higher borrowing capacity option		200,000,000
Debt Instrument, Term			5 years
Line of credit | Credit Agreement | Letter of Credit Sub-Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity		50,000,000
Line of credit | Credit Agreement | Bridge Loan | Graybar Canada
Line of Credit Facility [Line Items]
Maximum borrowing capacity		100,000,000
Line of credit | Credit Agreement | Bridge Loan | UNITED STATES
Line of Credit Facility [Line Items]
Maximum borrowing capacity		50,000,000
Line of credit | Credit Agreement | Bridge Loan | CANADA
Line of Credit Facility [Line Items]
Maximum borrowing capacity		20,000,000
Line of credit | Amended Credit Agreement | Minimum | Eurodollar [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate			1.00%
Line of credit | Amended Credit Agreement | Maximum | Eurodollar [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate			1.60%
Line of credit | Amended Credit Agreement | Revolving Credit Facility
Line of Credit Facility [Line Items]
Accordion feature, higher borrowing capacity option			300,000,000
Line of credit | Amended Credit Agreement | Revolving Credit Facility | Base Rate
Line of Credit Facility [Line Items]
Description of variable rate basis			base rate loans
Line of credit | Amended Credit Agreement | Revolving Credit Facility | Eurodollar [Member]
Line of Credit Facility [Line Items]
Description of variable rate basis			Eurodollar rate
Line of credit | Amended Credit Agreement | Revolving Credit Facility | Minimum
Line of Credit Facility [Line Items]
Credit agreement commitment fee percentage			0.25%
Line of credit | Amended Credit Agreement | Revolving Credit Facility | Minimum | Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate			0.00%
Line of credit | Amended Credit Agreement | Revolving Credit Facility | Maximum
Line of Credit Facility [Line Items]
Credit agreement commitment fee percentage			0.40%
Line of credit | Amended Credit Agreement | Revolving Credit Facility | Maximum | Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate			0.60%
Line of credit | Amended Credit Agreement | Letter of Credit Sub-Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity			50,000,000
Line of credit | Amended Credit Agreement | Bridge Loan | Graybar Canada
Line of Credit Facility [Line Items]
Maximum borrowing capacity			100,000,000
Line of credit | Amended Credit Agreement | Bridge Loan | UNITED STATES
Line of Credit Facility [Line Items]
Maximum borrowing capacity			50,000,000
Line of credit | Amended Credit Agreement | Bridge Loan | CANADA
Line of Credit Facility [Line Items]
Maximum borrowing capacity			20,000,000
Line of credit | Amended Credit Agreement | Letter of Credit | Minimum
Line of Credit Facility [Line Items]
Credit agreement commitment fee percentage			1.00%
Line of credit | Amended Credit Agreement | Letter of Credit | Maximum
Line of Credit Facility [Line Items]
Credit agreement commitment fee percentage			1.60%
Letter of Credit
Line of Credit Facility [Line Items]
Letters of credit outstanding	5,725,000	6,886,000
Letter of Credit | Revolving Credit Facility
Line of Credit Facility [Line Items]
Letters of credit outstanding	$ 0	$ 711,000