Revenue - Percentages of Sales by Product Line (Details) - Product Line - Sales	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Percentage of Sales by Product Line [Line Items]
Percentage of sales	100.00%	100.00%	100.00%	100.00%
Fasteners
Percentage of Sales by Product Line [Line Items]
Percentage of sales	33.70%	34.70%	34.30%	35.10%
Tools
Percentage of Sales by Product Line [Line Items]
Percentage of sales	10.20%	10.10%	10.00%	10.10%
Cutting tools
Percentage of Sales by Product Line [Line Items]
Percentage of sales	5.70%	5.70%	5.80%	5.70%
Hydraulics & pneumatics
Percentage of Sales by Product Line [Line Items]
Percentage of sales	6.80%	6.70%	6.90%	6.90%
Material handling
Percentage of Sales by Product Line [Line Items]
Percentage of sales	5.90%	5.70%	5.90%	5.80%
Janitorial supplies
Percentage of Sales by Product Line [Line Items]
Percentage of sales	8.00%	7.80%	7.70%	7.60%
Electrical supplies
Percentage of Sales by Product Line [Line Items]
Percentage of sales	4.60%	4.60%	4.70%	4.60%
Welding supplies
Percentage of Sales by Product Line [Line Items]
Percentage of sales	4.20%	4.10%	4.20%	4.10%
Safety Supplies
Percentage of Sales by Product Line [Line Items]
Percentage of sales	18.20%	17.30%	17.60%	17.00%
Other
Percentage of Sales by Product Line [Line Items]
Percentage of sales	2.70%	3.30%	2.90%	3.10%