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Stockholders' Equity - Additional Information (Detail) - USD ($)
 12 Months Ended
Jan. 05, 2018
Dec. 31, 2017
Dec. 31, 2016
Class of Stock [Line Items]      
Condition of electing directors by class a and class b common stock vote   In the election of directors, the holders of Class A common stock are entitled by class vote, exclusive of other stockholders, to elect two of the Company's directors, with each Class A share being entitled to one vote. In the election of the other six directors and all other matters submitted to the stockholders for a vote, the holders of Class A shares and Class B shares shall vote as a single class, with each Class A share being entitled to one vote and each Class B share entitled to ten votes.  
Aggregate amount permitted for share repurchases   $ 2,500,000  
Payments for treasury stock   $ 1,107,064 $ 198,152
Payments for treasury stock, shares   94,753  
Total leverage ratio   3.50%  
Cash dividends paid   $ 5,137,470 $ 4,140,864
Maximum [Member]      
Class of Stock [Line Items]      
Long-term debt covenants aggregate leverage ratio   2.5  
New Credit Agreement [Member] | Maximum [Member]      
Class of Stock [Line Items]      
Total leverage ratio   3.75%  
Leverage Ratio Less Than 3.5 [Member]      
Class of Stock [Line Items]      
Shares of common stock to be repurchased when leverage rate is greater than threshold specified   $ 7,500,000  
Leverage Ratio Greater Than or Equal to 3.5 [Member]      
Class of Stock [Line Items]      
Shares of common stock to be repurchased when leverage rate is greater than threshold specified   $ 10,000,000  
Class A Common Stock [Member]      
Class of Stock [Line Items]      
Dividend declared per share   $ 0.045  
Class B Common Stock [Member]      
Class of Stock [Line Items]      
Dividend declared per share   $ 0.045  
Subsequent Event [Member]      
Class of Stock [Line Items]      
Cash dividends paid $ 1,300,000