Purchase Agreement, Controlled Equity Offering and Public Offering of Common Stock - Additional Information (Detail) - USD ($)			4 Months Ended	12 Months Ended
	Aug. 31, 2017	Apr. 28, 2017	Apr. 27, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 16, 2016
Stockholders Equity Common Stock [Line Items]
Warrants to purchase common shares		24,900,000
Offering price		$ 1.00
Gross proceeds from public offering		$ 24,900,000
Net proceeds from public offering		$ 23,200,000
Warrants exercised		0
Lincoln Park Capital Fund, LLC [Member]
Stockholders Equity Common Stock [Line Items]
Right to sell common stock						25,000,000
Stock issued, shares				3,972,741	300,000
Gross proceeds				$ 5,304,000	$ 412,500
Proceeds from issuance of common stock, net of issuance costs				$ 5,304,000	$ 392,500
Stifel, Nicolaus & Company, Incorporated [Member]
Stockholders Equity Common Stock [Line Items]
Percentage of commission paid	3.00%
Stifel, Nicolaus & Company, Incorporated [Member] | Maximum [Member]
Stockholders Equity Common Stock [Line Items]
Sale of common stock in an at-the-market offering	$ 50,000,000
Commitment Shares [Member] | Lincoln Park Capital Fund, LLC [Member]
Stockholders Equity Common Stock [Line Items]
Stock issued, shares			345,421
Common Stock [Member]
Stockholders Equity Common Stock [Line Items]
Number of common stock or warrants in each unit		1
Common Stock [Member] | Series A Warrant [Member]
Stockholders Equity Common Stock [Line Items]
Number of common stock or warrants in each unit		1
Common Stock [Member] | Series B Warrant [Member]
Stockholders Equity Common Stock [Line Items]
Number of common stock or warrants in each unit		0.75