Quarterly report pursuant to Section 13 or 15(d)

Equity - Class B Common Stock (Detail)

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Equity - Class B Common Stock (Detail) - Class B Common Stock - shares
 1 Months Ended 3 Months Ended
Mar. 31, 2021
Jan. 31, 2021
Mar. 31, 2021
Mar. 31, 2020
Dec. 31, 2020
Dec. 31, 2019
Class Of Stock [Line Items]            
Common stock, shares outstanding 4,769,835   4,769,835 4,855,000 4,721,646 5,031,000
Issuance of Class B common stock upon vesting of restricted stock units   34,196 56,000      
Cancellation of Class B common stock upon conversion of Class B units to Class A common stock     8,000 176,000    
Common stock conversion date   2021-01        
Restricted Stock            
Class Of Stock [Line Items]            
Issuance of Class B common stock upon vesting of restricted stock units   21,598        
Common stock conversion date   2021-01        
Resale And Registration Rights Agreement            
Class Of Stock [Line Items]            
Cancellation of Class B common stock upon conversion of Class B units to Class A common stock (7,605)   (7,605)      
Common stock conversion date 2021-03