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Revenue - Percentages of Sales by Product Line (Details) - Product Line - Sales	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
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	34.80%	35.00%
Tools
Percentage of Sales by Product Line [Line Items]
Percentage of sales	9.90%	10.20%
Cutting tools
Percentage of Sales by Product Line [Line Items]
Percentage of sales	5.90%	5.70%
Hydraulics & pneumatics
Percentage of Sales by Product Line [Line Items]
Percentage of sales	6.90%	7.00%
Material handling
Percentage of Sales by Product Line [Line Items]
Percentage of sales	5.80%	5.80%
Janitorial supplies
Percentage of Sales by Product Line [Line Items]
Percentage of sales	7.50%	7.40%
Electrical supplies
Percentage of Sales by Product Line [Line Items]
Percentage of sales	4.70%	4.80%
Welding supplies
Percentage of Sales by Product Line [Line Items]
Percentage of sales	4.10%	4.20%
Safety Supplies
Percentage of Sales by Product Line [Line Items]
Percentage of sales	17.20%	16.80%
Other
Percentage of Sales by Product Line [Line Items]
Percentage of sales	3.20%	3.10%

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