Annual report pursuant to Section 13 and 15(d)

Equity - Summary of Authorized and Outstanding Equity (Parenthetical) (Detail)

v3.20.4
Equity - Summary of Authorized and Outstanding Equity (Parenthetical) (Detail) - $ / shares
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Class Of Stock [Line Items]        
Preferred stock, par value $ 0.01 $ 0.01    
Class A Common Stock        
Class Of Stock [Line Items]        
Common stock, par value $ 0.01 $ 0.01    
Common stock, voting rights one vote for each share      
Common stockholders rights percentage 100.00%      
Restricted stock units granted 8,242      
Restricted stock units unvested 8,242      
Common stock, shares outstanding 9,650,692 9,329,879 8,518,000 8,142,000
Class B Common Stock        
Class Of Stock [Line Items]        
Common stock, par value $ 0.01 $ 0.01    
Common stock, voting rights one vote for each share      
Restricted stock units granted 74,906      
Class of share exchangeable to another class one-for-one basis      
Common stock, shares outstanding 4,721,646 5,031,017 4,934,000 5,059,000