Purchase Agreement, Controlled Equity Offering and Public Offering of Common Stock - Additional Information (Detail) - USD ($)				3 Months Ended
	Dec. 28, 2018	Aug. 31, 2017	Apr. 28, 2017	Mar. 31, 2019
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
Stifel, Nicolaus & Company, Incorporated [Member]
Stockholders Equity Common Stock [Line Items]
Percentage of commission paid	3.00%	3.00%
Total shares of common stock sold				0
Stifel, Nicolaus & Company, Incorporated [Member] | Maximum [Member]
Stockholders Equity Common Stock [Line Items]
Sale of common stock in an at-the-market offering	$ 75,000,000	$ 50,000,000
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