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Treasury Stock - Additional Information (Detail) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2019
Mar. 31, 2019
Dec. 31, 2018
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Equity, Class of Treasury Stock [Line Items]            
Treasury stock, shares repurchased value   $ 48,244,000 $ 110,977,000      
Treasury stock, shares 7,648,000   7,285,000   7,648,000  
Treasury stock, cost $ 634,405,000   $ 586,161,000   $ 634,405,000  
Class A            
Equity, Class of Treasury Stock [Line Items]            
Treasury stock, shares repurchased   0 0      
Treasury stock, shares repurchased value   $ 0 $ 0      
Class A | Share Repurchase Program            
Equity, Class of Treasury Stock [Line Items]            
Shares repurchased program expiration date         Apr. 29, 2023  
Stock authorized to repurchase by board of directors $ 800,000,000.0       $ 800,000,000.0  
Treasury stock, shares repurchased 0     0 362,148 0
Shares repurchased, average price per share         $ 133.21  
Treasury stock, shares repurchased value         $ 48,200,000  
Treasury stock, shares 5,069,762       5,069,762  
Shares repurchased, average price per share $ 99.51       $ 99.51  
Treasury stock, cost $ 504,500,000       $ 504,500,000