XML 78 R64.htm IDEA: XBRL DOCUMENT v3.10.0.1
Share-Based Compensation - Summary of Performance-Based Option Activity (Detail) - Performance Shares [Member] - Share Based Compensation Plans [Member] - USD ($)
$ / shares in Units, $ in Millions
9 Months Ended 12 Months Ended
Sep. 30, 2018
Dec. 31, 2017
Shares    
Options Outstanding at Beginning of Period 1,038,147  
Options, Granted 0  
Options, Exercised (633,606)  
Options, Forfeited or expired (8,358)  
Options Outstanding at End of Period 396,183 1,038,147
Options Exercisable at End of Period 396,183  
Weighted Average Exercise Price (per share)    
Weighted Average Exercise Price at Beginning of Period $ 13.46  
Weighted Average Exercise Price, Granted 0  
Weighted Average Exercise Price, Exercised (13.46)  
Weighted Average Exercise Price, Forfeited or expired (13.46)  
Weighted Average Exercise Price at End of Period 13.50 $ 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 4 months 24 days 3 years 6 months
Weighted Average Remaining Contractual Term Exercisable (in years) 3 years 4 months 24 days  
Aggregate Intrinsic Value    
Aggregate Intrinsic Value, Options Outstanding $ 11.3  
Aggregate Intrinsic Value, Options Exercisable $ 11.3