Sales by Product Line (Percentages Of Sales By Product Line) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue from External Customer [Line Items]
Total, percentage of sales	100.00%	100.00%	100.00%
Fasteners [Member]
Revenue from External Customer [Line Items]
Introduced	1967
Total, percentage of sales	35.60%	36.60%	38.30%
Tools [Member]
Revenue from External Customer [Line Items]
Introduced	1993
Total, percentage of sales	10.10%	9.90%	9.50%
Cutting tools [Member]
Revenue from External Customer [Line Items]
Introduced	1996
Total, percentage of sales	5.80%	5.70%	5.60%
Hydraulics & pneumatics [Member]
Revenue from External Customer [Line Items]
Introduced	1996
Total, percentage of sales	6.80%	6.90%	7.20%
Material handling [Member]
Revenue from External Customer [Line Items]
Introduced	1996
Total, percentage of sales	6.30%	6.40%	6.50%
Janitorial supplies [Member]
Revenue from External Customer [Line Items]
Introduced	1996
Total, percentage of sales	7.60%	7.60%	7.50%
Electrical supplies [Member]
Revenue from External Customer [Line Items]
Introduced	1997
Total, percentage of sales	4.90%	4.80%	4.70%
Welding supplies [Member]
Revenue from External Customer [Line Items]
Introduced	1997
Total, percentage of sales	4.60%	4.60%	4.70%
Safety supplies [Member]
Revenue from External Customer [Line Items]
Introduced	1999
Total, percentage of sales	15.20%	14.90%	13.90%
Metals [Member]
Revenue from External Customer [Line Items]
Introduced	2001
Total, percentage of sales	0.50%	0.50%	0.50%
Direct ship [Member]
Revenue from External Customer [Line Items]
Introduced	2004
Total, percentage of sales	0.50%	0.50%	0.40%
Office supplies [Member]
Revenue from External Customer [Line Items]
Introduced	2010
Total, percentage of sales	0.10%	0.10%	0.10%
Other product line [Member]
Revenue from External Customer [Line Items]
Total, percentage of sales	2.00%	1.50%	1.10%