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Summary of All Stock Option Activity (Detail) - Stock Option - USD ($)
$ / shares in Units, $ in Millions
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Options Outstanding at December 31, 2015 1,820,956  
Exercised, Number of Options (417,442)  
Forfeited, Number of Options (17,300)  
Expired, Number of Options (112,460)  
Options Outstanding at December 31, 2016 1,273,754 1,820,956
Options Exercisable at December 31, 2016 1,093,165  
Options Outstanding, Weighted Average Grant Date Fair Value $ 11.61  
Exercised, Weighted Average Exercise Price 11.57  
Forfeited, Weighted Average Exercise Price 14.64  
Expired, Weighted Average Exercise Price 16.71  
Options Outstanding, Weighted Average Grant Date Fair Value 11.13 $ 11.61
Options Exercisable,Weighted Average Exercise Price, at December 31, 2016 $ 10.67  
Options Outstanding,Weighted Average Remaining Contractual Life 5 years 1 month 6 days 5 years 2 months 12 days
Options Exercisable, Weighted Average Remaining Contractual Life, at December 31, 2016 4 years 7 months 6 days  
Options Outstanding, Aggregate Intrinsic Value $ 6.0 $ 2.3
Options Exercised, Aggregate Intrinsic Value 1.3  
Options Exercisable, Aggregate Intrinsic Value $ 5.6