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Long-term Incentive Plan - Summary of Long-term Incentive Plan (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Disclosure of long-term incentive plan [abstract]    
Opening balance $ 18.1 $ 23.6
Charge to income statement - continuing operations 1.1 5.0
Charge to income statement - discontinued operations 0.0 0.1
Payments (17.8) (11.5)
Translation adjustment 0.7 0.9
Balance at end of the year 2.1 18.1
Current portion of long-term incentive plan 0.0 (18.1)
Non-current portion of long-term incentive plan $ 2.1 $ 0.0