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
Mar. 31, 2018
Jan. 31, 2018
Dec. 31, 2017
Mar. 31, 2017
Dec. 31, 2016
Class Of Stock [Line Items]          
Common stock, shares outstanding 8,259,056   8,142,120 8,100,000 8,074,000
Issuance of Class A common stock upon conversion of Class B units to Class A common stock 85,286 31,650      
Common stock conversion date Mar. 31, 2018 Jan. 31, 2018