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Revenue - Percentages of Sales by Product Line (Details) - Product Line - Sales | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Percentage of Sales by Product Line [Line Items] |  |  |
Percentage of sales | 100.00% | 100.00% | 100.00%
Fasteners |  |  |
Percentage of Sales by Product Line [Line Items] |  |  |
Percentage of sales | 34.20% | 34.90% | 35.60%
Tools |  |  |
Percentage of Sales by Product Line [Line Items] |  |  |
Percentage of sales | 9.90% | 10.00% | 10.10%
Cutting tools |  |  |
Percentage of Sales by Product Line [Line Items] |  |  |
Percentage of sales | 5.70% | 5.70% | 5.80%
Hydraulics and pneumatics |  |  |
Percentage of Sales by Product Line [Line Items] |  |  |
Percentage of sales | 6.80% | 6.80% | 6.80%
Material handling |  |  |
Percentage of Sales by Product Line [Line Items] |  |  |
Percentage of sales | 5.90% | 5.80% | 5.90%
Janitorial supplies |  |  |
Percentage of Sales by Product Line [Line Items] |  |  |
Percentage of sales | 7.80% | 7.60% | 7.30%
Electrical supplies |  |  |
Percentage of Sales by Product Line [Line Items] |  |  |
Percentage of sales | 4.70% | 4.70% | 4.90%
Welding supplies |  |  |
Percentage of Sales by Product Line [Line Items] |  |  |
Percentage of sales | 4.20% | 4.10% | 4.20%
Safety supplies |  |  |
Percentage of Sales by Product Line [Line Items] |  |  |
Percentage of sales | 17.90% | 17.20% | 16.30%
Other |  |  |
Percentage of Sales by Product Line [Line Items] |  |  |
Percentage of sales | 2.90% | 3.20% | 3.10%

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