Annual report pursuant to Section 13 and 15(d)

Equity - Class B Common Stock (Detail)

v3.8.0.1
Equity - Class B Common Stock (Detail) - Class B Common Stock - shares
 1 Months Ended 12 Months Ended
Nov. 30, 2017
Aug. 31, 2017
Jun. 30, 2017
May 31, 2017
Mar. 31, 2017
May 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Class Of Stock [Line Items]                    
Common stock conversion date 2017-11 2017-08     2017-03          
Stock issued upon vesting of stock units   2017-08   2017-05   2016-05        
Common stock issuance date     2017-06              
Common stock, shares outstanding             5,059,319 4,866,303 4,695,000 4,520,000
Cancellation of Class B common stock upon conversion of Class B units to Class A common stock             63,000 84,000 211,000  
Class B common stock issued   241,628 13,468 947   947 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 (10,900) (24,119)   (2,000) (26,008)