Stockholders' Equity - Additional Information (Detail) - USD ($)					3 Months Ended
	May 09, 2017	Apr. 21, 2017	Apr. 17, 2017	Jan. 04, 2017	Mar. 31, 2017	Mar. 31, 2016	Apr. 30, 2017
Stockholders Equity [Line Items]
Aggregate gross proceeds from sale of common stock					$ 5,267,000	$ 127,000
Equity Distribution Agreement | Citigroup Global Markets Inc. | ATM Offering
Stockholders Equity [Line Items]
Aggregate gross proceeds from sale of common stock					$ 6,400,000
Common Stock | Equity Distribution Agreement | Citigroup Global Markets Inc. | ATM Offering
Stockholders Equity [Line Items]
Sale of common stock shares					4,264,970
Maximum | Equity Distribution Agreement | Citigroup Global Markets Inc. | ATM Offering
Stockholders Equity [Line Items]
Aggregate value of common stock available				$ 50,000,000
Percentage of sales agent commission on gross proceeds				3.00%
Reimbursement of sales agent expenses				$ 50,000
Weighted Average | Common Stock | Equity Distribution Agreement | Citigroup Global Markets Inc. | ATM Offering
Stockholders Equity [Line Items]
Average market price per share					$ 1.51
Subsequent Event
Stockholders Equity [Line Items]
Aggregate gross proceeds from sale of common stock	$ 75,500,000
Subsequent Event | Citigroup Global Markets Inc. and Leerink Partners LLC | Underwritten Public Offering
Stockholders Equity [Line Items]
Percentage of underwriter discounts and commissions on per share offering price			6.00%
Subsequent Event | Equity Distribution Agreement | Citigroup Global Markets Inc. | ATM Offering
Stockholders Equity [Line Items]
Aggregate gross proceeds from sale of common stock	$ 900,000
Proceeds from sale of common stock not yet received							$ 900,000
Subsequent Event | Common Stock | Citigroup Global Markets Inc. and Leerink Partners LLC | Underwritten Public Offering
Stockholders Equity [Line Items]
Sale of common stock shares		69,000,000	60,000,000
Aggregate gross proceeds from sale of common stock		$ 74,600,000
Public offering price per share			$ 1.15
Subsequent Event | Common Stock | Equity Distribution Agreement | Citigroup Global Markets Inc. | ATM Offering
Stockholders Equity [Line Items]
Sale of common stock shares	625,262
Subsequent Event | Maximum | Common Stock | Citigroup Global Markets Inc. and Leerink Partners LLC | Underwritten Public Offering
Stockholders Equity [Line Items]
Additional sale of common stock shares			9,000,000
Subsequent Event | Weighted Average | Common Stock | Equity Distribution Agreement | Citigroup Global Markets Inc. | ATM Offering
Stockholders Equity [Line Items]
Average market price per share	$ 1.46