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Stock Buy Back Plans - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Feb. 02, 2016
Equity Class Of Treasury Stock [Line Items]        
Purchase of treasury shares     $ 100,000,000  
Class A Common Stock [Member]        
Equity Class Of Treasury Stock [Line Items]        
Stock repurchase program, authorized amount       $ 100,000,000
Stock repurchase program expiration date Dec. 31, 2016      
Purchase of treasury shares (in shares) 0 0 2,672,227  
Class A Common Stock [Member] | Employee Restricted Stock Plan [Member]        
Equity Class Of Treasury Stock [Line Items]        
Stock tendered for payments of withholding taxes (in shares) 87,381 77,988    
Purchase of treasury shares $ 4,300,000 $ 3,400,000