Convertible Preferred Stock and Stockholders' Equity (Deficit) - Additional Information (Detail)		9 Months Ended
	May 24, 2017 shares	Sep. 30, 2017 vote shares
Temporary Equity [Line Items]
Convertible preferred stock outstanding shares converted into common stock		1
Class B Common Stock
Temporary Equity [Line Items]
Conversion of convertible preferred stock to common stock (in shares)	18,163,158
Convertible preferred stock outstanding shares converted into common stock		1
Preferred stock conversion basis		1
Number of votes entitled to stockholders | vote		10
Class A Common Stock
Temporary Equity [Line Items]
Number of votes entitled to stockholders | vote		1
Conversion of stock (in shares)		1
Maximum percentage of aggregate voting power of capital stock which triggers conversion of stock		10.00%