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Equity - Additional Information (Detail) - USD ($)
 1 Months Ended 11 Months Ended 12 Months Ended
Feb. 28, 2016
Nov. 30, 2014
Sep. 30, 2015
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Disclosure of equity [line items]            
Dividend payable annual percentage 40.00%          
Dividends payable per share       $ 0.80 $ 0.65  
Treasury stock [member]            
Disclosure of equity [line items]            
Share repurchase program authorized amount   $ 250,000,000        
Number of shares repurchase program     2,310,492      
Share repurchase program period value     $ 136,400,000      
Accelerated share repurchase [member]            
Disclosure of equity [line items]            
Share repurchase program period value         $ 113,600,000  
Class A common stock [member]            
Disclosure of equity [line items]            
Common stock, shares authorised       80,000,000    
Common stock, shares issued       33,861,872 33,835,747  
Common stock, shares outstanding       31,421,265 31,337,856 31,257,686
Class B common stock [member]            
Disclosure of equity [line items]            
Common stock, shares authorised       80,000,000    
Common stock, shares issued       10,938,125 10,938,125  
Common stock, shares outstanding       10,938,125 10,938,125 10,938,125
Class C common stock [member]            
Disclosure of equity [line items]            
Common stock, shares authorised       80,000,000    
Common stock, shares outstanding       0 0