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Goodwill and Identifiable Assets (Goodwill) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Apr. 02, 2018	Dec. 31, 2017
Goodwill [Roll Forward]
Gross goodwill	$ 1,445.6		$ 1,421.1		$ 894.1
Goodwill, Acquired During Period	24.7	$ 528.2
Translation adjustment	(0.2)	(1.2)
Goodwill	1,445.6		1,421.1
Apex
Goodwill [Roll Forward]
Gross goodwill	662.1		662.1		662.1
Oxford
Goodwill [Roll Forward]
Gross goodwill	230.6		230.8		$ 232.0
Translation adjustment	(0.2)	(1.2)
ECS
Goodwill [Roll Forward]
Gross goodwill	552.9		$ 528.2
DHA \| DHA
Goodwill [Roll Forward]
Goodwill, Acquired During Period	$ 24.7
ECS
Goodwill [Roll Forward]
Goodwill				$ 528.2
ECS \| ECS
Goodwill [Roll Forward]
Goodwill, Acquired During Period		$ 528.2