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Restricted Stock, Performance Share and Cash Awards - Additional Information (Detail)
 3 Months Ended
Mar. 31, 2018
USD ($)
shares
Mar. 31, 2017
USD ($)
shares
Mar. 16, 2017
USD ($)
shares
Mar. 31, 2016
shares
Dec. 31, 2017
shares
Mar. 17, 2016
USD ($)
shares
Mar. 11, 2015
USD ($)
shares
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]              
Share-based compensation, shares outstanding | shares 9,800,000       9,500,000    
Provisional compensation cash award approved for future grant by compensation committee, units | shares 269,000 199,000          
Grants vested in period fair value $ 15,800,000 $ 9,300,000          
Long Term Incentive Plan [Member]              
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]              
Share-based compensation, shares outstanding, Value $ 4,000,000            
Share-based compensation, shares outstanding | shares 3,500,000            
Shares granted in the period | shares 3,500,000            
Restricted Stock Units (RSUs) [Member]              
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]              
Shares granted in the period | shares 420,200 477,500          
Fair value of grants in period $ 28,700,000 $ 26,800,000          
Share based payment award vesting date Mar. 15, 2022 Mar. 16, 2021          
Restricted stock or unit expense $ 6,500,000 $ 4,000,000          
Restricted Stock Units (RSUs) [Member] | Minimum [Member]              
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]              
Period of service from grant date stock options awarded not subject to forfeiture 2 years 2 years          
Restricted Stock Units (RSUs) [Member] | Executive Officer [Member] | Minimum [Member]              
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]              
Minimum age of employee with not subject to award forfeiture on condition compliance 55 years 55 years          
Unvested Restricted Stock [Member]              
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]              
Total intrinsic value $ 121,900,000 $ 90,400,000          
Equity awards with an aggregate fair value 21,200,000 18,800,000          
Performance Shares [Member]              
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]              
Equity awards with an aggregate fair value $ 3,700,000 $ 2,800,000          
Shares authorized | shares 78,200 86,250          
Performance unit awards approved, Fair value $ 5,300,000 $ 4,900,000          
Provisional awards, terms Granted units for the 2018 and 2017 provisional awards will fully vest based on continuous employment through March 16, 2021 and 2020, respectively, and will be settled in shares of our common stock on a one-for-one basis as soon as practicable thereafter.            
Performance awards expiration date Mar. 15, 2021 Mar. 16, 2020          
Performance awards period, years 3 years 3 years          
Vesting period, years 3 years 3 years          
Performance Shares [Member] | Minimum [Member]              
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]              
Period of service from grant date stock options awarded not subject to forfeiture 2 years 2 years          
Performance Shares [Member] | Executive Officer [Member] | Minimum [Member]              
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]              
Minimum age of employee with not subject to award forfeiture on condition compliance 55 years 55 years          
2017 Provisional Cash Awards [Member]              
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]              
Performance awards expiration date Jan. 01, 2020            
Cash-based compensation awards, expenses $ 2,000,000   $ 0        
2017 Provisional Cash Awards [Member] | Officer and Key Employees [Member]              
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]              
Provisional compensation cash awards approved for future grant by compensation committee, value     $ 14,300,000        
Provisional compensation cash award approved for future grant by compensation committee, units | shares 242,000   255,000        
2016 Provisional Cash Awards [Member]              
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]              
Performance awards expiration date   Jan. 01, 2019          
Cash-based compensation awards, expenses $ 4,200,000 $ 2,600,000          
2016 Provisional Cash Awards [Member] | Officer and Key Employees [Member]              
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]              
Provisional compensation cash awards approved for future grant by compensation committee, value           $ 17,400,000  
Provisional compensation cash award approved for future grant by compensation committee, units | shares   383,000       397,000  
Cash Awards [Member] | Officer and Key Employees [Member]              
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]              
Provisional awards, terms The ultimate award value will be equal to the trailing twelve-month price of our common stock on December 31, 2020, multiplied by the number of units subject to the award, but limited to between 0.5 and 1.5 times the original value of the units determined as of the grant date.            
Performance awards period, years 1 year            
Vesting period, years 2 years            
Provisional compensation cash awards approved for future grant by compensation committee, value $ 15,000,000            
Provisional compensation cash award approved for future grant by compensation committee, units | shares 219,000            
Ultimate award value, multiples of original value of the units, minimum 0.5            
Ultimate award value, multiples of original value of the units, maximum 1.5            
2018 Provisional Cash Awards [Member]              
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]              
Performance awards expiration date Jan. 01, 2021            
Cash-based compensation awards, expenses $ 0            
2015 Provisional Cash Awards [Member]              
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]              
Performance awards expiration date       Jan. 01, 2018      
Cash-based compensation awards, expenses   $ 3,100,000          
2015 Provisional Cash Awards [Member] | Officer and Key Employees [Member]              
Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]              
Provisional compensation cash awards approved for future grant by compensation committee, value             $ 14,600,000
Provisional compensation cash award approved for future grant by compensation committee, units | shares       294,000     315,000