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Share-Based Compensation - Summary of Performance-Based Option Activity (Detail) - Performance Shares [Member] - Share Based Compensation Plans [Member] - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Shares        
Options Outstanding at Beginning of Period 1,038,147 1,230,426 1,283,368  
Options, Granted 0 0 0  
Options, Exercised (663,412) (167,202) 0  
Options, Forfeited or expired (8,358) (25,077) (52,942)  
Options Outstanding at End of Period 366,377 1,038,147 1,230,426 1,283,368
Options Exercisable at End of Period 366,377      
Weighted Average Exercise Price (per share)        
Weighted Average Exercise Price at Beginning of Period $ 13.46 $ 13.46 $ 13.46  
Weighted Average Exercise Price, Granted 0 0 0  
Weighted Average Exercise Price, Exercised (13.46) (13.46) 0  
Weighted Average Exercise Price, Forfeited or expired (13.46) (13.46) (13.46)  
Weighted Average Exercise Price at End of Period 13.50 $ 13.46 $ 13.46 $ 13.46
Weighted Average Exercise Price Exercisable at End of Period $ 13.50      
Weighted Average Remaining Contractual Term (in years)        
Weighted Average Remaining Contractual Term (in years) 3 years 1 month 6 days 3 years 6 months 4 years 2 months 12 days 5 years 2 months 12 days
Weighted Average Remaining Contractual Term Exercisable (in years) 3 years 1 month 6 days      
Aggregate Intrinsic Value        
Aggregate Intrinsic Value, Options Outstanding $ 7.7      
Aggregate Intrinsic Value, Options Exercisable $ 7.7