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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 |  |  |

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