Revenue - Percentages of Sales by Product Line (Details) - Product Line - Sales	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
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	32.90%	34.80%
Tools
Percentage of Sales by Product Line [Line Items]
Percentage of sales	9.40%	9.90%
Cutting tools
Percentage of Sales by Product Line [Line Items]
Percentage of sales	5.40%	5.90%
Hydraulics & pneumatics
Percentage of Sales by Product Line [Line Items]
Percentage of sales	6.60%	6.90%
Material handling
Percentage of Sales by Product Line [Line Items]
Percentage of sales	5.70%	5.80%
Janitorial supplies
Percentage of Sales by Product Line [Line Items]
Percentage of sales	8.30%	7.50%
Electrical supplies
Percentage of Sales by Product Line [Line Items]
Percentage of sales	4.60%	4.70%
Welding supplies
Percentage of Sales by Product Line [Line Items]
Percentage of sales	4.10%	4.10%
Safety Supplies
Percentage of Sales by Product Line [Line Items]
Percentage of sales	19.80%	17.20%
Other
Percentage of Sales by Product Line [Line Items]
Percentage of sales	3.20%	3.20%