Convertible Preferred Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended
	Apr. 19, 2018	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Convertible Preferred Stock [Line Items]
Preferred stock conversion rate	100.00%
Convertible preferred stock, shares outstanding			0	0
Series A Convertible Preferred Stock | 2018 Direct Registered Offering
Convertible Preferred Stock [Line Items]
Convertible preferred stock, shares issued		3,000,581
Stock price		$ 8.31
Convertible preferred stock, beneficial conversion feature		$ 2.7
Number of preferred stock converted into common stock	3,000,581