Quarterly report pursuant to Section 13 or 15(d)

Earnings Per Share - Additional Information (Detail)

v3.10.0.1
Earnings Per Share - Additional Information (Detail) - shares
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Earnings Per Share [Line Items]        
Options excluded from the computation of diluted earnings since they are antidilutive 407,267 25,556 335,885 51,470
Class A Common Stock [Member]        
Earnings Per Share [Line Items]        
Common stock, voting rights     One vote per share  
Class B Common Stock [Member]        
Earnings Per Share [Line Items]        
Common stock, voting rights     Ten votes per share