Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Statement [Abstract]
Net sales	$ 2,991.6	$ 2,747.4	$ 8,254.3	$ 7,671.5
Cost of goods sold	2,820.0	2,596.0	7,786.5	7,252.4
Gross profit	171.6	151.4	467.8	419.1
Warehousing and distribution expenses	92.8	83.5	260.9	236.9
Selling, general and administrative expenses	52.8	47.0	147.6	134.9
Amortization of intangible assets	0.6	0.7	1.8	2.0
Total operating expenses	146.2	131.2	410.3	373.8
Income from operations	25.4	20.2	57.5	45.3
Interest expense	(0.6)	(0.5)	(1.9)	(1.8)
Interest income	0.1	0.1	0.4	0.4
Foreign currency transaction gains (losses), net	(0.7)	0.2	(1.3)	0.0
Income before income taxes	24.2	20.0	54.7	43.9
Provision for income taxes	(9.1)	(6.3)	(20.9)	(15.8)
Net income	$ 15.1	$ 13.7	$ 33.8	$ 28.1
Basic net income per common share (in dollars per share)	$ 0.65	$ 0.59	$ 1.46	$ 1.22
Diluted net income per common share (in dollars per share)	$ 0.65	$ 0.59	$ 1.45	$ 1.21
Basic weighted-average shares	23.1	23.1	23.1	23.1
Diluted weighted-average shares	23.3	23.3	23.3	23.2
Dividends declared per common share (in dollars per share)	$ 0.13	$ 0.11	$ 0.39	$ 0.33
Dividends paid per common share (in dollars per share)	$ 0.13	$ 0.11	$ 0.39	$ 0.33