Condensed Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Net sales	$ 4,495.9	$ 4,263.9	$ 8,428.1	$ 8,203.2
Cost of goods sold	4,252.2	4,050.8	7,967.0	7,771.7
Gross profit	243.7	213.1	461.1	431.5
Warehousing and distribution expenses	147.0	125.5	284.3	267.9
Selling, general and administrative expenses	68.1	59.8	131.5	123.7
Amortization of intangible assets	2.6	2.4	5.3	4.7
Total operating expenses	217.7	187.7	421.1	396.3
Income from operations	26.0	25.4	40.0	35.2
Interest expense, net	(2.4)	(2.8)	(5.5)	(6.3)
Foreign currency transaction gains (losses), net	0.2	0.0	0.4	(0.2)
Income before income taxes	23.8	22.6	34.9	28.7
Provision for income taxes	(8.3)	(5.7)	(10.9)	(7.5)
Net income	$ 15.5	$ 16.9	$ 24.0	$ 21.2
Basic earnings per share (in dollars per share) (Note 6)	$ 0.34	$ 0.38	$ 0.53	$ 0.47
Diluted earnings per share (in dollars per share) (Note 6)	$ 0.34	$ 0.38	$ 0.53	$ 0.47
Basic weighted-average shares (in shares) (Note 6)	45.2	45.1	45.2	45.2
Diluted weighted-average shares (in shares) (Note 6)	45.5	45.3	45.4	45.4