Stockholders' Equity - Common Stock - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Nov. 30, 2017
Sale Of Stock [Line Items]
Common stock, shares issued	24,231,914		17,427,533
Proceeds from issuance of common stock, net	$ 5,800,201	$ 4,618,297
FBR Sales Agreement [Member]
Sale Of Stock [Line Items]
Common stock, shares issued	6,804,381	1,985,054
Common stock , weighted average price per share	$ 0.87	$ 2.38
Proceeds from issuance of common stock, net	$ 5,800,000	$ 4,600,000
FBR Sales Agreement [Member] | Maximum [Member]
Sale Of Stock [Line Items]
Common stock, value of shares issuable				$ 16,000,000