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Earnings Per Share - Additional Information (Detail) - shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Earnings Per Share [Line Items]      
Class B common stock conversion, number of shares 2,581,627 2,601,996 2,711,811
Anti-dilutive stock options excluded from earnings per share 74,270 11,664 31,839