Subsequent Events - Additional Information (Detail) - USD ($)			1 Months Ended		12 Months Ended	23 Months Ended
	Feb. 25, 2016	Aug. 11, 2015	Feb. 29, 2016	Nov. 30, 2014	Dec. 31, 2015	Dec. 31, 2015
Subsequent Event [Line Items]
Gross proceeds of financing				$ 21,000,000		$ 17,500,000
Common stock, shares issued				30,941,102		24,859,107
Securities offered and sold combination					These securities were offered and sold to the underwriters and the public in units with each Series A unit consisting of one share of our common stock and one-half (0.5) of a warrant and each Series B unit consisting of one pre-funded warrant and one-half (0.5) of a warrant.
Net proceeds from financing				$ 19,700,000		$ 16,600,000
Exercise price of warrants per share				$ 0.75
Warrants exercisable period				Nov. 12, 2019
Warrants issued to purchase shares of common stock				22,011,265	77,385,622	77,385,622
Warrants to Hercules [Member]
Subsequent Event [Line Items]
Exercise price of warrants per share					$ 0.41	$ 0.41
Warrants exercisable period					Aug. 11, 2020
Warrants issued to purchase shares of common stock					1,524,390	1,524,390
Loan and Security Agreement [Member] | Hercules [Member]
Subsequent Event [Line Items]
Payments of debt issuance costs		$ 112,500
Subsequent Event [Member]
Subsequent Event [Line Items]
Gross proceeds of financing			$ 8,000,000
Common stock, shares issued			29,090,910
Securities offered and sold combination			each consisting of one share of our common stock and one warrant to purchase one share of our common stock.
Number of securities in each unit issued			1
Number of common stock called by each warrant			1
Net proceeds from financing			$ 7,300,000
Exercise price of warrants per share			$ 0.42
Warrants exercisable period			Aug. 17, 2016
Warrants expiration date			Feb. 16, 2021
Subsequent Event [Member] | Second Amendment | Warrants to Hercules [Member]
Subsequent Event [Line Items]
Exercise price of warrants per share	$ 0.275
Warrants issued to purchase additional shares of common stock	748,337
Warrants issued to purchase shares of common stock	2,272,727
Subsequent Event [Member] | Loan and Security Agreement [Member] | Hercules [Member]
Subsequent Event [Line Items]
Prepayments of outstanding principal	$ 10,000,000
Subsequent Event [Member] | Loan and Security Agreement [Member] | Hercules [Member] | Third Amendment [Member]
Subsequent Event [Line Items]
Payments of debt issuance costs	$ 37,500