Convertible Preferred Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended
	Mar. 31, 2018	Sep. 30, 2018	Apr. 19, 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