Credit Agreement (Details) - USD ($)		12 Months Ended
	Jun. 06, 2014	Dec. 31, 2015	Dec. 31, 2014
Line of Credit Facility [Line Items]
Fixed rate debt carrying amount in excess of fair value		$ 1,243,000	$ 1,331,000
Remaining borrowing capacity		$ 445,022,000	$ 483,658,000
Credit agreement commitment fee percentage		0.40%	0.40%
Line of credit | Credit Agreement | Minimum | Eurodollar [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.00%
Line of credit | Credit Agreement | Maximum | Eurodollar [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.60%
Line of credit | Credit Agreement | Revolving Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 550,000,000
Accordion feature, higher borrowing capacity option	$ 300,000,000
Debt Instrument, Term	5 years
Line of credit | Credit Agreement | Revolving Credit Facility | Base Rate
Line of Credit Facility [Line Items]
Description of variable rate basis	base rate loans
Line of credit | Credit Agreement | Revolving Credit Facility | Eurodollar [Member]
Line of Credit Facility [Line Items]
Description of variable rate basis	Eurodollar rate
Line of credit | Credit Agreement | Revolving Credit Facility | Minimum
Line of Credit Facility [Line Items]
Credit agreement commitment fee percentage	0.25%
Line of credit | Credit Agreement | Revolving Credit Facility | Minimum | Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.00%
Line of credit | Credit Agreement | Revolving Credit Facility | Maximum
Line of Credit Facility [Line Items]
Credit agreement commitment fee percentage	0.40%
Line of credit | Credit Agreement | Revolving Credit Facility | Maximum | Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.60%
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 | Credit Agreement | Letter of Credit | Minimum
Line of Credit Facility [Line Items]
Credit agreement commitment fee percentage	1.00%
Line of credit | 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		$ 4,994,000	$ 5,725,000
Letter of Credit | Revolving Credit Facility
Line of Credit Facility [Line Items]
Letters of credit outstanding		$ 0	$ 0