Stockholders' Equity - Common Stock - Additional Information (Detail) - USD ($)	1 Months Ended	2 Months Ended	9 Months Ended
	Oct. 31, 2018	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Nov. 30, 2017
Sale Of Stock [Line Items]
Proceeds from issuance of common stock, net			$ 4,618,297	$ 7,389,101
Common stock, shares issued			17,427,533		15,413,610
Underwritten Public Offering [Member]
Sale Of Stock [Line Items]
Common stock shares issues		2,775,861
Purchase price of common stock		$ 2.90
Gross proceeds from public offering of common stock		$ 8,000,000
Proceeds from issuance of common stock, net		$ 7,300,000
FBR Sales Agreement [Member]
Sale Of Stock [Line Items]
Proceeds from issuance of common stock, net			$ 4,600,000
Common stock, shares issued			1,985,054
Common stock , weighted average price per share			$ 2.38
FBR Sales Agreement [Member] | Maximum [Member]
Sale Of Stock [Line Items]
Common stock, value of shares issuable						$ 16,000,000
Entity public float			$ 75,000,000
FBR Sales Agreement [Member] | Subsequent Event [Member]
Sale Of Stock [Line Items]
Additional common stock, shares issued	0
Entity public float	$ 47,800,000
Entity public float, common stock shares	14,349,303
Common stock, closing price	$ 3.33
Proceeds from issuance of additional common stock	$ 11,200,000