Stockholders' Equity - Common Stock - Additional Information (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Nov. 30, 2017
Sale Of Stock [Line Items]
Common stock, shares issued	24,113,956		17,427,533
Proceeds from issuance of common stock, net	$ 5,676,388	$ 3,431,520
FBR Sales Agreement [Member]
Sale Of Stock [Line Items]
Common stock, shares issued	6,686,423	1,485,054
Common stock , weighted average price per share	$ 0.87	$ 2.38
Proceeds from issuance of common stock, net	$ 5,700,000	$ 3,400,000
FBR Sales Agreement [Member] | Maximum [Member]
Sale Of Stock [Line Items]
Common stock, value of shares issuable				$ 16,000,000