Condensed Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income Statement [Abstract]
Net sales	$ 2,810.4	$ 2,623.2	$ 5,262.7	$ 4,924.1
Cost of goods sold	2,651.5	2,479.9	4,966.5	4,656.4
Gross profit	158.9	143.3	296.2	267.7
Warehousing and distribution expenses	88.6	78.1	168.1	153.4
Selling, general and administrative expenses	47.5	44.0	94.8	87.9
Amortization of intangible assets	0.6	0.7	1.2	1.3
Total operating expenses	136.7	122.8	264.1	242.6
Income from operations	22.2	20.5	32.1	25.1
Interest expense	(0.7)	(0.6)	(1.3)	(1.3)
Interest income	0.1	0.2	0.3	0.3
Foreign currency transaction losses, net	(0.2)	(0.2)	(0.6)	(0.2)
Income before income taxes	21.4	19.9	30.5	23.9
Provision for income taxes	(8.2)	(7.9)	(11.8)	(9.5)
Net income	$ 13.2	$ 12.0	$ 18.7	$ 14.4
Basic net income per common share (in dollars per share)	$ 0.57	$ 0.52	$ 0.81	$ 0.63
Diluted net income per common share (in dollars per share)	$ 0.57	$ 0.52	$ 0.81	$ 0.62
Basic weighted-average shares	23.1	23.1	23.1	23.1
Diluted weighted-average shares	23.3	23.2	23.3	23.2
Dividends declared per common share (in dollars per share)	$ 0.13	$ 0.11	$ 0.26	$ 0.22
Dividends paid per common share (in dollars per share)	$ 0.13	$ 0.11	$ 0.26	$ 0.22