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Revenue - Percentages of Sales by Product Line (Details) - Product Line - Sales	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Percentage of Sales by Product Line [Line Items]
Percentage of sales	100.00%	100.00%
Fasteners
Percentage of Sales by Product Line [Line Items]
Percentage of sales	35.00%	35.60%
Tools
Percentage of Sales by Product Line [Line Items]
Percentage of sales	10.20%	10.20%
Cutting tools
Percentage of Sales by Product Line [Line Items]
Percentage of sales	5.70%	5.90%
Hydraulics & pneumatics
Percentage of Sales by Product Line [Line Items]
Percentage of sales	7.00%	6.90%
Material handling
Percentage of Sales by Product Line [Line Items]
Percentage of sales	5.80%	6.10%
Janitorial supplies
Percentage of Sales by Product Line [Line Items]
Percentage of sales	7.40%	7.30%
Electrical supplies
Percentage of Sales by Product Line [Line Items]
Percentage of sales	4.80%	4.70%
Welding supplies
Percentage of Sales by Product Line [Line Items]
Percentage of sales	4.20%	4.30%
Safety Supplies
Percentage of Sales by Product Line [Line Items]
Percentage of sales	16.80%	16.00%
Other
Percentage of Sales by Product Line [Line Items]
Percentage of sales	3.10%	3.00%

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