Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
Net sales	$ 3,993.9	$ 2,991.6	$ 10,692.6	$ 8,254.3
Cost of goods sold	3,795.0	2,820.0	10,154.7	7,786.5
Gross profit	198.9	171.6	537.9	467.8
Warehousing and distribution expenses	117.4	92.8	315.0	260.9
Selling, general and administrative expenses	57.6	52.8	160.0	147.6
Amortization of intangible assets	1.7	0.6	3.8	1.8
Total operating expenses	176.7	146.2	478.8	410.3
Income from operations	22.2	25.4	59.1	57.5
Interest expense	(1.5)	(0.6)	(3.3)	(1.9)
Interest income	0.0	0.1	0.1	0.4
Foreign currency transaction losses , net	(0.5)	(0.7)	(0.1)	(1.3)
Income before income taxes	20.2	24.2	55.8	54.7
Provision for income taxes	(6.7)	(9.1)	(20.3)	(20.9)
Net income	$ 13.5	$ 15.1	$ 35.5	$ 33.8
Basic net income per common share (in dollars per share)	$ 0.29	$ 0.33	$ 0.77	$ 0.73
Diluted net income per common share (in dollars per share)	$ 0.29	$ 0.33	$ 0.76	$ 0.73
Basic weighted-average shares (in shares)	46.3	46.2	46.3	46.2
Diluted weighted-average shares (in shares)	46.5	46.6	46.5	46.6
Dividends declared and paid per common share (in dollars per share)	$ 0.08	$ 0.07	$ 0.24	$ 0.20
Dividends paid per common share (usd per share)	$ 0.08	$ 0.07	$ 0.24	$ 0.20