Condensed Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Net sales	$ 4,310.7	$ 3,993.9	$ 11,615.6	$ 10,692.6
Cost of goods sold	4,088.5	3,795.0	11,033.3	10,154.7
Gross profit	222.2	198.9	582.3	537.9
Warehousing and distribution expenses	137.4	117.4	370.1	315.0
Selling, general and administrative expenses	57.0	57.6	166.5	160.0
Amortization of intangible assets	2.4	1.7	6.0	3.8
Total operating expenses	196.8	176.7	542.6	478.8
Income from operations	25.4	22.2	39.7	59.1
Interest expense	(3.9)	(1.5)	(7.9)	(3.3)
Interest income	0.1	0.0	0.2	0.1
Foreign currency transaction gains (loss), net	0.2	(0.5)	1.9	(0.1)
Income before income taxes	21.8	20.2	33.9	55.8
Provision for income taxes	(8.1)	(6.7)	(11.2)	(20.3)
Net income	$ 13.7	$ 13.5	$ 22.7	$ 35.5
Basic net income per common share (in dollars per share)	$ 0.29	$ 0.29	$ 0.49	$ 0.77
Diluted net income per common share (in dollars per share)	$ 0.29	$ 0.29	$ 0.49	$ 0.76
Basic weighted-average shares (in shares)	46.3	46.3	46.3	46.3
Diluted weighted-average shares (in shares)	46.4	46.5	46.4	46.5
Dividends declared per common share (in dollars per share)	$ 0.09	$ 0.08	$ 0.27	$ 0.24
Dividends paid per common share (usd per share)	$ 0.09	$ 0.08	$ 0.27	$ 0.24