Stockholders' Equity - Summary of Stock Option and Warrant Activity under 2005 Equity Incentive Plan and Warrants Issued Outside of Plan to Employees and Consultants (Detail) - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options or Warrants, Balance outstanding, Beginning Balance	1,914,906
Number of Options or Warrants, Granted	5,534,692
Number of Options or Warrants, Cancelled (unvested)	(60,000)
Number of Options or Warrants, Expired (vested)	(35,750)
Number of Options or Warrants, Balance outstanding, Ending Balance	7,353,848	1,914,906
Number of Options or Warrants, Exercisable, Ending Balance	7,093,841
Weighted Average Exercise Price, Balance outstanding, Beginning Balance	$ 2.44
Weighted Average Exercise Price, Granted	0.67
Weighted Average Exercise Price, Cancelled(unvested)	0.60
Weighted Average Exercise Price, Expired (vested)	24.11
Weighted Average Exercise Price, Balance outstanding, Ending Balance	1.02	$ 2.44
Weighted Average Exercise Price, Exercisable, Ending Balance	$ 1.04
Weighted Average Remaining Contractual Life (in years), Balance	8 years 10 months 6 days	8 years 8 months 27 days
Weighted Average Remaining Contractual Life (in years), Granted	9 years 1 month 6 days
Weighted Average Remaining Contractual Life (in years), Exercisable, Ending Balance	8 years 9 months 29 days