Quarterly report pursuant to Section 13 or 15(d)

Equity - Treasury Stock (Detail)

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Equity - Treasury Stock (Detail) - USD ($)
shares in Millions
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Equity, Class of Treasury Stock [Line Items]          
Repurchase of common stock $ 15,993,000 $ 0 $ 189,906,000 $ 0  
2017 Repurchase Program          
Equity, Class of Treasury Stock [Line Items]          
Treasury stock acquired (in shares) 0.6   5.6   1.4
Treasury stock acquired, value $ 20,000,000   $ 193,900,000   $ 50,000,000
Repurchase of common stock 16,000,000   189,900,000    
2017 Repurchase Program | Maximum          
Equity, Class of Treasury Stock [Line Items]          
Aggregate authorized amount of common stock to be repurchased   300,000,000   300,000,000  
Treasury Stock Associated with Deferred Compensation Plans          
Equity, Class of Treasury Stock [Line Items]          
Treasury stock acquired, value $ 0 $ 200,000 $ 3,300,000 $ 3,400,000  
Common Stock Withheld for Settlement of Employee Tax Liabilities          
Equity, Class of Treasury Stock [Line Items]          
Treasury stock acquired (in shares)     0.4 0.5  
Treasury stock acquired, value     $ 14,200,000 $ 17,800,000