Stockholders' Equity - Summary of Stock Option and Warrant Activities Issued to Employees and Directors (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Deferred Compensation Arrangement With Individual Share Based Payments [Line Items]
Number of Options or Warrants, Balance outstanding, Beginning Balance	8,054,346
Number of Options or Warrants, Balance outstanding, Ending Balance	12,116,334	8,054,346
Directors and Employees [Member]
Deferred Compensation Arrangement With Individual Share Based Payments [Line Items]
Number of Options or Warrants, Balance outstanding, Beginning Balance	7,337,598	1,914,906
Number of Options or Warrants, Granted	4,823,736	5,534,692
Number of Options or Warrants, Cancelled (unvested)		(60,000)
Number of Options or Warrants, Expired (vested)	(45,000)	(52,000)
Number of Options or Warrants, Balance outstanding, Ending Balance	12,116,334	7,337,598	1,914,906
Number of Options or Warrants, Exercisable, Ending Balance	12,110,078
Weighted Average Exercise Price, Balance outstanding, Beginning Balance	$ 0.94	$ 2.44
Weighted Average Exercise Price, Granted	0.71	0.67
Weighted Average Exercise Price, Cancelled (unvested)		0.60
Weighted Average Exercise Price, Expired (vested)	0.73	28.76
Weighted Average Exercise Price, Balance outstanding, Ending Balance	0.73	$ 0.94	$ 2.44
Weighted Average Exercise Price, Exercisable, Ending Balance	$ 0.73
Weighted Average Remaining Contractual Life (in years), Balance	7 years 8 months 2 days	8 years 7 months 13 days	8 years 8 months 26 days
Weighted Average Remaining Contractual Life (in years), Granted	7 years 9 months	8 years 10 months 6 days
Weighted Average Remaining Contractual Life (in years), Exercisable, Ending Balance	7 years 8 months 2 days