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	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options or Warrants, Balance outstanding, Beginning Balance	7,337,598
Number of Options or Warrants, Expired (vested)	(45,000)
Number of Options or Warrants, Balance outstanding, Ending Balance	7,292,598	7,337,598
Number of Options or Warrants, Exercisable, Ending Balance	7,034,091
Weighted Average Exercise Price, Balance outstanding, Beginning Balance	$ 0.94
Weighted Average Exercise Price, Expired (vested)	32.67
Weighted Average Exercise Price, Balance outstanding, Ending Balance	0.74	$ 0.94
Weighted Average Exercise Price, Exercisable, Ending Balance	$ 0.75
Weighted Average Remaining Contractual Life (in years), Balance	8 years 5 months 1 day	8 years 7 months 13 days
Weighted Average Remaining Contractual Life (in years), Exercisable, Ending Balance	8 years 4 months 24 days