Revenue - Percentages of Sales by Product Line (Details) - Product Line - Sales	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 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	34.50%	35.40%	34.70%	35.20%
Tools
Percentage of Sales by Product Line [Line Items]
Percentage of sales	9.80%	9.90%	9.90%	10.00%
Cutting tools
Percentage of Sales by Product Line [Line Items]
Percentage of sales	5.80%	5.60%	5.80%	5.70%
Hydraulics & pneumatics
Percentage of Sales by Product Line [Line Items]
Percentage of sales	6.80%	6.90%	6.90%	6.90%
Material handling
Percentage of Sales by Product Line [Line Items]
Percentage of sales	5.90%	5.90%	5.90%	5.80%
Janitorial supplies
Percentage of Sales by Product Line [Line Items]
Percentage of sales	7.70%	7.60%	7.60%	7.50%
Electrical supplies
Percentage of Sales by Product Line [Line Items]
Percentage of sales	4.70%	4.60%	4.70%	4.70%
Welding supplies
Percentage of Sales by Product Line [Line Items]
Percentage of sales	4.20%	4.10%	4.20%	4.20%
Safety Supplies
Percentage of Sales by Product Line [Line Items]
Percentage of sales	17.50%	16.90%	17.40%	16.90%
Other
Percentage of Sales by Product Line [Line Items]
Percentage of sales	3.10%	3.10%	2.90%	3.10%