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Treasury Stock - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Equity, Class of Treasury Stock [Line Items]      
Treasury stock, shares repurchased value $ 110,977,000    
Treasury stock, shares 7,285,000 6,405,000  
Treasury stock, cost $ 586,161,000 $ 475,184,000  
Class A      
Equity, Class of Treasury Stock [Line Items]      
Treasury stock, shares repurchased 0    
Treasury stock, shares repurchased value $ 0    
Class A | 2005 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    
Treasury stock, shares repurchased 880,667 0 0
Shares repurchased, average price per share $ 126.02    
Treasury stock, shares repurchased value $ 111,000,000    
Treasury stock, shares 4,707,614    
Shares repurchased, average price per share $ 96.92    
Treasury stock, cost $ 456,300,000