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 6 Months Ended
Jun. 30, 2017
May 31, 2017
Mar. 31, 2017
Jun. 30, 2017
Jun. 30, 2016
Dec. 31, 2016
Dec. 31, 2015
Class Of Stock [Line Items]              
Common stock conversion date   2017-05 2017-03        
Stock issued upon vesting of stock units   2017-05          
Common stock issuance date 2017-06            
Common stock, shares outstanding 4,852,711     4,852,711 4,671,000 4,866,303 4,695,000
Cancellation of Class B common stock upon conversion of Class B units to Class A common stock       28,000 38,000    
Class B common stock issued 13,468 948   13,000      
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   (2,000) (26,008)