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Share-Based Compensation - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Shares issuable upon exercise of outstanding options 2,868,053 3,085,888 2,657,723 3,781,964
Number of shares to reduce shares available to grant by upon vesting of restricted stock awards and units 1,453,823 1,712,204 757,871 598,892
Estimated pretax compensation expense $ 5.0      
Expiration period in years 4 years      
Service period in years 4 years      
Restricted stock units settled in cash exercisable in percentage 25.00%      
Stock compensation and recognized liability $ 4.1 $ 5.6 $ 1.4  
Long-term incentive, cash-based awards 3 years      
Performance unit award expenses $ 5.3 $ 5.4 $ 2.1  
Volatility assumptions for estimating the fair value of stock options, minimum 63.90%      
Volatility assumptions for estimating the fair value of stock options, maximum 65.20%      
Share-based Compensation Award, Tranche Two [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Stock awards settled in stock exercisable in percentage 33.33%      
Share-based Compensation Award, Tranche Three [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Stock awards settled in stock exercisable in percentage 33.33%      
Non-Employee Directors' Stock Options [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Expiration period in years 10 years      
Employee stock options exercisable in percentage 100.00%      
Employee Stock Option [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Expiration period in years 10 years      
Service period in years 4 years      
Employee Stock Option [Member] | Share-based Compensation Award, Tranche One [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Stock awards settled in stock exercisable in percentage 25.00%      
Restricted Stock Shares [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Number of shares to reduce shares available to grant by upon vesting of restricted stock awards and units       42,752
Service period in years 4 years      
Restricted Stock Shares [Member] | Share-based Compensation Award, Tranche One [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Service period in years 3 years      
Restricted Stock Shares [Member] | Share-based Compensation Award, Tranche Two [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Service period in years 3 years      
Restricted Stock Shares [Member] | Share-based Compensation Award, Tranche Three [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Service period in years 3 years      
Restricted Stock Units [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Number of shares to reduce shares available to grant by upon vesting of restricted stock awards and units 1,453,823 1,712,204 757,871 556,140
Restricted Stock Units [Member] | Share-based Compensation Award, Tranche One [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Stock awards settled in stock exercisable in percentage 20.00%      
Restricted Stock Units [Member] | Share-based Compensation Award, Tranche Two [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Stock awards settled in stock exercisable in percentage 50.00%      
Restricted Stock Units [Member] | Share-based Compensation Award, Tranche Three [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Stock awards settled in stock exercisable in percentage 30.00%      
Deferred Stock Units to be Settled in Shares [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Service period in years 3 years      
2016 Incentive Compensation Plan [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Common stock subject to awards of stock options or stock appreciation rights payable in shares 1.0      
Common stock subject to any other form of award 1.35      
Common stock available for future share-based awards 4,000,000      
Shares issuable upon exercise of outstanding options 500,000      
Number of shares to reduce shares available to grant by upon vesting of restricted stock awards and units 400,000      
2008 Incentive Compensation Plan [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Shares issuable upon exercise of outstanding options 2,400,000      
Number of shares to reduce shares available to grant by upon vesting of restricted stock awards and units 1,300,000      
2008 Incentive Compensation Plan [Member] | Chief Executive Officer [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Service period in years 2 years      
Restricted stock units settled in cash exercisable in percentage 50.00%