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Share-Based Compensation - Narrative (Detail) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2017
Mar. 31, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Share-based compensation       $ 6.4 $ 13.4
Restricted stock units          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Annual share-based compensation grants   569,594   102,191  
Grant date fair value   $ 16.30   $ 11.77  
Graded vesting period   3 years      
Weighted average vesting period       1 year 6 months  
Performance share units          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Annual share-based compensation grants   304,425      
Grant date fair value   $ 16.30      
Cliff vesting period   34 months      
Continuing operations          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Share-based compensation $ 2.1   $ 2.1 $ 6.4 $ 7.9