Stockholders' Equity - Common Stock - Additional Information (Detail) - USD ($)	1 Months Ended	2 Months Ended	6 Months Ended
	Aug. 03, 2018	Mar. 31, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Nov. 30, 2017
Sale Of Stock [Line Items]
Proceeds from issuance of common stock, net			$ 3,431,520	$ 7,332,239
Common stock, shares issued			16,898,664		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			$ 3,400,000
Common stock, shares issued			1,485,054
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	$ 45,700,000
Entity public float, common stock shares	15,932,051
Common stock, closing price	$ 2.87
Proceeds from issuance of additional common stock	$ 11,700,000