Equity Line Financing, Controlled Equity Offering and Public Offering of Common Stock - Additional Information (Detail) - USD ($)				1 Months Ended		3 Months Ended		12 Months Ended	33 Months Ended
	Dec. 16, 2016	Feb. 09, 2016	Feb. 20, 2015	Apr. 26, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2016	Nov. 30, 2014	Jan. 31, 2014
Stockholders Equity Common Stock [Line Items]
Proceeds from issuance of common stock, net of issuance costs						$ 5,304,000	$ 31,391,000
Common stock, shares issued						123,629,689		115,781,030	115,781,030
Aggregate maximum value of designated securities										$ 100,000,000	$ 100,000,000
Increase in value of designated securities					$ 50,000,000
Gross proceeds from public offering of securities									$ 179,200,000
Proceeds from issuance of common stock from public offering, net of issuance costs									$ 168,800,000
Amount available for future financing of common stock						$ 37,800,000
ATM Offering [Member]
Stockholders Equity Common Stock [Line Items]
Amount available for future financing of common stock						$ 2,400,000
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
Additional common stock shares issued on a pro rata basis	119,551
Gross proceeds						$ 5,304,000		$ 412,500
Proceeds from issuance of common stock, net of issuance costs						5,304,000		$ 392,500
Amount available for future financing of common stock						19,500,000
Lincoln Park Capital Fund, LLC [Member] | Subsequent Event [Member]
Stockholders Equity Common Stock [Line Items]
Gross proceeds				$ 5,700,000
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