Convertible Preferred Stock and Stockholders' Equity (Deficit) - Summary of Activity for Convertible Preferred Stock Issued and Outstanding (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Increase (Decrease) in Temporary Equity [Roll Forward]
Payment of accrued dividend to Series A convertible preferred stockholders	$ (7,565)	$ 0
Series A Convertible Preferred Stock
Increase (Decrease) in Temporary Equity [Roll Forward]
Beginning balance, January 1, 2017	$ 17,915
Beginning balance, shares issued	12,043,108
Accretion of dividends on convertible preferred stock	$ 357
Payment of accrued dividend to Series A convertible preferred stockholders	$ (7,565)
Conversion of convertible preferred stock to common stock (in shares)	(12,043,108)
Conversion of convertible preferred stock to common stock	$ (10,707)
Ending balance, September 30, 2017	$ 0
Ending balance, shares issued	0
Series B Convertible Preferred Stock
Increase (Decrease) in Temporary Equity [Roll Forward]
Beginning balance, January 1, 2017	$ 37,500
Beginning balance, shares issued	6,120,050
Accretion of dividends on convertible preferred stock	$ 0
Payment of accrued dividend to Series A convertible preferred stockholders	$ 0
Conversion of convertible preferred stock to common stock (in shares)	(6,120,050)
Conversion of convertible preferred stock to common stock	$ (37,500)
Ending balance, September 30, 2017	$ 0
Ending balance, shares issued	0