Equity Line Financing, Controlled Equity Offering and Public Offering of Common Stock - Additional Information (Detail) - USD ($)					4 Months Ended	9 Months Ended	12 Months Ended
	Aug. 31, 2017	Apr. 28, 2017	Feb. 09, 2016	Feb. 20, 2015	Apr. 27, 2017	Sep. 30, 2017	Dec. 31, 2016	Dec. 16, 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
Common stock, shares issued						155,283,207	115,781,030
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
Cantor Fitzgerald & Co. [Member]
Stockholders Equity Common Stock [Line Items]
Gross proceeds			$ 25,000,000
Proceeds from issuance of common stock, net of issuance costs			$ 24,000,000
Percentage of commission paid			3.00%	3.00%
Common stock, shares issued			7,724,488
Agreement termination date						Sep. 10, 2017
Cantor Fitzgerald & Co. [Member] | Maximum [Member]
Stockholders Equity Common Stock [Line Items]
Sale of common stock in an at-the-market offering			$ 43,600,000	$ 25,000,000
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
Series A Warrant [Member]
Stockholders Equity Common Stock [Line Items]
Warrants exercised						5,204,495
Series B Warrant [Member]
Stockholders Equity Common Stock [Line Items]
Warrants exercised						0
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