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Stock-Based Compensation - Summary of Stock Options Outstanding (Detail) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]      
Number of Options, Stock options outstanding, Beginning Balance 6,338,000    
Number of Options, Stock options granted 0    
Number of Options, Stock options exercised (742,000) (283,000) (60,000)
Number of Options, Stock options forfeited (70,000)    
Number of Options, Stock options expired (378,000)    
Number of Options, Stock options outstanding, Ending Balance 5,148,000 6,338,000  
Number of Options, Stock options vested and expected to vest 5,148,000    
Number of Options, Stock options exercisable 4,351,000    
Weighted Average Exercise Price, Stock options outstanding, Beginning Balance $ 22.14    
Weighted Average Exercise Price, Stock options exercised 18.08    
Weighted Average Exercise Price, Stock options forfeited 17.29    
Weighted Average Exercise Price, Stock options expired 24.14    
Weighted Average Exercise Price, Stock options outstanding, Ending Balance 22.65 $ 22.14  
Weighted Average Exercise Price, Stock options vested and expected to vest 22.65    
Weighted Average Exercise Price, Stock options exercisable $ 23.78    
Weighted Avg. Remaining Contractual Life in Years, Stock options outstanding 4 years 10 months 13 days 5 years 7 months 17 days  
Weighted Avg. Remaining Contractual Life in Years, Stock options vested and expected to vest 4 years 10 months 13 days    
Weighted Avg. Remaining Contractual Life in Years, Stock options exercisable 4 years 4 months 13 days    
Aggregate Intrinsic Value, Stock options outstanding $ 6,109 $ 16,972  
Aggregate Intrinsic Value, Stock options vested and expected to vest 6,109    
Aggregate Intrinsic Value, Stock options exercisable $ 3,810