Debt - Credit Agreement (Details) - USD ($)		3 Months Ended
	Aug. 10, 2018	Mar. 31, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity		$ 529,500,000	$ 515,000,000
Commitment fee percentage		0.40%
Line of Credit | Credit Agreement [Member] | Revolving Credit Facility
Line of Credit Facility [Line Items]
Debt Instrument, Term	5 years
Maximum borrowing capacity	$ 750,000,000
Accordion feature, higher borrowing capacity option	375,000,000
Line of Credit | Credit Agreement [Member] | Letter of Credit Sub-Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity	25,000,000
Line of Credit | Credit Agreement [Member] | Bridge Loan | Graybar Canada
Line of Credit Facility [Line Items]
Maximum borrowing capacity	100,000,000
Line of Credit | Credit Agreement [Member] | Bridge Loan | UNITED STATES
Line of Credit Facility [Line Items]
Maximum borrowing capacity	75,000,000
Line of Credit | Credit Agreement [Member] | Bridge Loan | CANADA
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 20,000,000
Letter of Credit
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount		$ 5,600,000	5,600,000
Letter of Credit | Revolving Credit Facility
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount		$ 500,000	$ 0