Stock Option Activity (Detail) (USD $)	6 Months Ended
	Jun. 30, 2012
Number of Shares
Number of Shares, Outstanding at beginning of period	1,771,705
Number of Shares, Granted	1,541,767
Number of Shares, Exercised
Number of Shares, Forfeited and canceled	(106,833)
Number of Shares, Outstanding at end of period	3,206,639
Number of Shares, Exercisable at end of period	1,589,016
Weighted average exercise price
Weighted average exercise price, Outstanding at beginning of period	$ 1.93
Weighted average exercise price, Granted	$ 0.95
Weighted average exercise price, Exercised
Weighted average exercise price, Forfeited and canceled	$ 3.20
Weighted average exercise price, Outstanding at end of period	$ 1.41
Weighted average exercise price, Exercisable at end of period	$ 1.81
Weighted average remaining contract term
Weighted average remaining contract term, Outstanding at end of period	8 years 37 days
Weighted average remaining contract term, Exercisable at end of period	6 years 256 days
Intrinsic Value
Intrinsic Value, Outstanding at end of period	$ 21,715
Intrinsic Value, Exercisable at end of period	$ 21,715