Unaudited Quarterly Financial Results (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended									12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	[1]	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues	$ 1,025.2	$ 1,002.7	$ 972.3	$ 923.7	$ 929.7	$ 906.4	$ 878.5		$ 685.2	$ 3,923.9	$ 3,399.8	$ 2,626.0
Gross profit	289.5	291.4	285.2	263.9	272.0	270.1	263.9		217.7	1,130.0	1,023.7	850.1
Income from continuing operations	39.3	57.5	43.1	34.9	46.0	49.1	33.7		29.2	174.8	158.0	157.9
Income from discontinued operations, net of income taxes										(0.1)	(0.3)	(0.2)
Net income	$ 39.3	$ 57.4	$ 43.1	$ 34.9	$ 45.9	$ 49.1	$ 33.6		$ 29.1	$ 174.7	$ 157.7	$ 157.7
Earnings per share:
Basic	$ 0.75	$ 1.09	$ 0.82	$ 0.66	$ 0.88	$ 0.94	$ 0.64		$ 0.56	$ 3.31	$ 3.02	$ 3.01
Diluted	$ 0.74	$ 1.08	$ 0.81	$ 0.66	$ 0.86	$ 0.93	$ 0.63		$ 0.55	$ 3.28	$ 2.98	$ 2.97
Discontinued Operations, Disposed of by Sale [Member]
Income from discontinued operations, net of income taxes	$ 0.0	$ (0.1)	$ 0.0	$ 0.0	$ (0.1)	$ 0.0	$ (0.1)		$ (0.1)	$ (0.1)	$ (0.3)

[1] ECS was acquired on April 2, 2018, see Note 4 – Acquisitions.