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Stock-based Compensation Plans - Additional Information 2 (Detail) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Stock-based compensation expense   $ 82,776 [1] $ 55,618 $ 57,801
Accelerated vesting of equity grants $ 30,800 30,800    
Proceeds from the sales of common stock held by the deferred compensation plan   $ 4,482 $ 13,102 $ 8,298
Restricted Stock Equity Awards        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Granted   888,326 973,491 587,711
Vesting period   3 years 3 years 3 years
Stock-based compensation expense   $ 23,400 $ 22,800 $ 23,800
Unrecognized compensation related to Awards 24,400 $ 24,400    
Weighted average period   1 year 8 months 12 days    
Granted, weighted average grant date fair value   $ 32.61 $ 28.51 $ 52.29
Restricted Stock Liability Awards        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Granted   543,438 540,128 343,397
Stock-based compensation expense   $ 30,400 $ 18,600 $ 20,800
Unrecognized compensation related to Awards $ 1,700 $ 1,700    
Weighted average period   1 year 7 months 6 days    
Granted, weighted average grant date fair value   $ 25.91 $ 35.92 $ 55.92
Accelerated vesting of equity grants   $ 15,400    
Restricted Stock Liability Awards | Non Employee Director        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Granted   90,000 59,000 48,000
Restricted Stock Liability Awards | Employees        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Granted   453,000 481,000 295,000
Vesting period   3 years 3 years 3 years
[1] Includes $30.8 million accelerated vesting of equity grants.