Summary of Activity under Stock-Based Compensation Plans (Detail) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Shares Available for Grant
Beginning Balance	3,854,194	7,769,039	7,769,039
Authorized
Granted	(2,767,952)		(2,276,747)
Cancelled or Expired	247,902		(1,638,098)
Ending Balance	1,334,144		3,854,194
Stock Options Number Outstanding
Beginning Balance	5,465,539	4,048,972	4,048,972
Amount of non-qualified stock options granted	2,680,000		2,115,725
Cancelled or Expired	(299,997)		(698,970)
Exercised	(2,625)	0	(188)
Ending Balance	7,842,917		5,465,539
Vested or expected to vest at March 31, 2014	6,717,775
Exercisable at March 31, 2014	3,110,282
Stock Options Average Exercise Price per share
Beginning Balance	$ 1.49	$ 1.94	$ 1.94
Granted	$ 0.88		$ 0.76
Cancelled or Expired	$ 1.64		$ 1.87
Exercised	$ 0.72		$ 0.72
Ending Balance	$ 1.28		$ 1.49
Vested or expected to vest at March 31, 2014	$ 1.35
Exercisable at March 31, 2014	$ 1.94
Stock Options Aggregate Intrinsic Value
Beginning Balance	$ 49,016	$ 825,309	$ 825,309
Ending Balance	1,624,221		49,016
Vested or expected to vest at March 31, 2014	1,265,851
Exercisable at March 31, 2014	131,638
Remaining Contractual Life (in years)
Beginning Balance	6 years 11 months 5 days	7 years 5 months 5 days	7 years 5 months 5 days
Ending Balance	7 years 5 months 27 days		6 years 11 months 5 days
Vested or expected to vest at March 31, 2014	7 years 1 month 21 days
Exercisable at March 31, 2014	4 years 7 months 2 days
Stock Awards Number Granted
Granted	87,952		161,022
Stock Awards Fair Value
Granted	$ 84,035		$ 135,600