Quarterly report pursuant to Section 13 or 15(d)

Equity - Class A Common Stock (Detail)

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Equity - Class A Common Stock (Detail) - Class A Common Stock - shares
1 Months Ended
Aug. 31, 2017
May 31, 2017
Apr. 30, 2017
Mar. 31, 2017
Sep. 30, 2017
Dec. 31, 2016
Sep. 30, 2016
Dec. 31, 2015
Class Of Stock [Line Items]                
Common stock, shares outstanding         8,131,220 8,074,197 8,049,000 7,990,000
Issuance of Class A common stock upon conversion of Class B units to Class A common stock 24,119 2,000   26,008        
Issuance of Class B shares, Shares   3,896 1,000          
Common stock conversion date Aug. 31, 2017 May 31, 2017   Mar. 31, 2017        
Stock issued upon vesting of stock units   2017-05 2017-04