Public Offerings of Common Stock - Additional Information (Detail) - USD ($)						9 Months Ended
	Feb. 09, 2016	Jul. 10, 2015	Jun. 11, 2015	Feb. 20, 2015	Apr. 30, 2014	Sep. 30, 2016	Sep. 30, 2015	Mar. 03, 2016	Mar. 02, 2016	Dec. 31, 2015	Apr. 14, 2014
Stockholders Equity Common Stock [Line Items]
Total shares of common stock sold						115,086,256				100,180,872
Net Proceeds		$ 5,800,000	$ 46,400,000		$ 52,400,000	$ 57,637,000	$ 58,295,000
Common stock to be sold, shares			16,666,667								12,500,000
Public offering price		$ 3.00	$ 3.00		$ 4.00						$ 4.00
Expected aggregate gross proceeds			$ 50,000,000								$ 50,000,000
Over-allotment option, shares to be issued to underwriters			2,500,000								1,875,000
Shares issued from option exercise by underwriters		2,075,000			1,610,000
Additional proceeds from exercise of option by underwriters		$ 6,200,000			$ 6,400,000
Proceeds from issuance of common stock from public offering, net of issuance costs						52,200,000
Issuance costs of Issuance of common shares					4,000,000	4,000,000
Aggregate maximum value of designated securities to be sold					$ 100,000,000	100,000,000		$ 150,000,000	$ 100,000,000
Value of stock to be purchased by existing stockholders											$ 10,000,000
Amount available for future financing of common stock						$ 71,200,000
Cantor Fitzgerald & Co. [Member]
Stockholders Equity Common Stock [Line Items]
Sale of common stock in an at-the-market offering	43,600,000			25,000,000
Percentage of commission paid	3.00%			3.00%
Total shares of common stock sold	7,724,488
Gross proceeds	$ 25,000,000
Net Proceeds	$ 24,000,000