Subsequent Events - Additional Information (Detail) - USD ($)	Oct. 31, 2017	Aug. 31, 2017	Apr. 28, 2017	Sep. 30, 2017
Subsequent Event [Line Items]
Warrants to purchase common shares			24,900,000
Offering price			$ 1.00
Stifel, Nicolaus & Company, Incorporated [Member]
Subsequent Event [Line Items]
Percentage of commission paid		3.00%
Stifel, Nicolaus & Company, Incorporated [Member] | Maximum [Member]
Subsequent Event [Line Items]
Sale of common stock in an at-the-market offering		$ 50,000,000
Subsequent Event [Member] | Stifel, Nicolaus & Company, Incorporated [Member]
Subsequent Event [Line Items]
Gross proceeds	$ 50,000,000
Proceeds from issuance of common stock, net of issuance costs	48,500,000
Series A Warrant [Member]
Subsequent Event [Line Items]
Warrants, exercise price			$ 1.00
Warrant expiration date			Oct. 31, 2017
Series A Warrant [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Gross proceeds from warrants exercised	$ 24,900,000
Series B Warrant [Member]
Subsequent Event [Line Items]
Warrants, exercise price			$ 1.00	$ 1.00
Series B Warrant [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Warrants to purchase common shares	8,900,000
Gross proceeds from warrants exercised	$ 8,700,000
Common Stock [Member]
Subsequent Event [Line Items]
Number of common stock or warrants in each unit			1
Common Stock [Member] | Series A Warrant [Member]
Subsequent Event [Line Items]
Number of common stock or warrants in each unit			1
Warrants, exercise price			$ 1.00
Common Stock [Member] | Series B Warrant [Member]
Subsequent Event [Line Items]
Number of common stock or warrants in each unit			0.75
Warrants, exercise price			$ 1.00