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Capitalization - Common and Preferred Stock (Detail)
 1 Months Ended 4 Months Ended 12 Months Ended
Sep. 30, 2016
Class
Vote
Dec. 31, 2016
Class
$ / shares
shares
Dec. 31, 2017
Class
$ / shares
shares
Class of Stock [Line Items]      
Number of classes of common stock | Class 2 2 2
Conversion of convertible Class B common stock to Class A common stock   4,200,000 21,800,000
Common stock, authorized shares     1,095,000,000
Common stock, par value (in dollars per share) | $ / shares   $ 0.000001 $ 0.000001
Preferred stock, authorized shares   100,000,000 100,000,000
Preferred stock, par value (in dollars per share) | $ / shares   $ 0.000001 $ 0.000001
Preferred stock, shares outstanding   0 0
Class B common stock      
Class of Stock [Line Items]      
Number of votes per share of common stock | Vote 10    
Ratio for conversion into Class A common stock 1    
Threshold percentage of aggregate outstanding common shares to trigger conversion 10.00%    
Threshold percentage vote or written consent of holders to trigger conversion 66.67%    
Common stock, authorized shares   95,000,000 95,000,000
Class A common stock      
Class of Stock [Line Items]      
Number of votes per share of common stock | Vote 1    
Common stock, authorized shares   1,000,000,000 1,000,000,000