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Consolidated Balance Sheets (Parenthetical) - USD ($)
Dec. 31, 2020
Dec. 31, 2019
Allowance for doubtful accounts $ 5,033,035 $ 2,145,599
Preferred stock, par value $ 0.001 $ 0.001
Preferred stock, shares authorized 10,000,000 10,000,000
Preferred stock, shares issued 0 0
Treasury stock, Class A common stock shares 3,253,691 4,493,181
Class A Common Stock [Member]    
Common stock, par value $ 0.001 $ 0.001
Common stock, shares authorized 150,000,000 150,000,000
Common stock, shares issued 15,930,765 15,805,432
Common stock, shares outstanding 12,677,074 11,312,251
Class B Common Stock [Member]    
Common stock, par value $ 0.001 $ 0.001
Common stock, shares authorized 75,000,000 75,000,000
Common stock, shares issued 16,662,743 16,662,743
Common stock, shares outstanding 16,662,743 16,662,743