Equity Line Financing, Controlled Equity Offering and Public Offering of Common Stock - Additional Information (Detail) - USD ($)					4 Months Ended	6 Months Ended	12 Months Ended
	Apr. 28, 2017	Dec. 16, 2016	Feb. 09, 2016	Feb. 20, 2015	Apr. 27, 2017	Jun. 30, 2017	Dec. 31, 2016
Stockholders Equity Common Stock [Line Items]
Warrants to purchase common shares	24,900,000
Public offering price	$ 1.00
Gross proceeds from public offering	$ 24,900,000
Net proceeds from public offering	$ 23,200,000
Warrants exercised	0					0
Common stock, shares issued						148,538,492	115,781,030
Lincoln Park Capital Fund, LLC [Member]
Stockholders Equity Common Stock [Line Items]
Right to sell common stock		25,000,000
Term to purchase number of shares		36 months
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
Cantor Fitzgerald & Co. [Member]
Stockholders Equity Common Stock [Line Items]
Gross proceeds			$ 25,000,000			$ 0
Proceeds from issuance of common stock, net of issuance costs			$ 24,000,000
Sale of common stock in an at-the-market offering			43,600,000	25,000,000
Percentage of commission paid			3.00%	3.00%
Common stock, shares issued			7,724,488
Maximum [Member] | Lincoln Park Capital Fund, LLC [Member]
Stockholders Equity Common Stock [Line Items]
Right to direct to purchase number of shares		150,000
Obligation under regular purchase of shares		$ 2,000,000
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