Summary of Option Activity (Detail) (Stock Options, USD $)	6 Months Ended
	Jun. 30, 2012
2005 Stock Incentive Plan
Stock Option
Outstanding at January 1, 2012	7,412,746
Granted	3,428,000
Exercised	(47,034)
Canceled	(1,370,312)
Outstanding at June 30, 2012	9,423,400
Shares exercisable at June 30, 2012	3,148,169
Shares available for grant at June 30, 2012	5,437,536
Weighted average exercise price
Outstanding at January 1, 2012	$ 2.22
Granted	$ 1.28
Exercised	$ 0.56
Canceled	$ 2.28
Outstanding at June 30, 2012	$ 1.88
Shares exercisable at June 30, 2012	$ 2.39
Stock Option Plan 1995
Stock Option
Outstanding at January 1, 2012	474,650
Canceled	(184,000)
Outstanding at June 30, 2012	290,650
Shares exercisable at June 30, 2012	290,650
Weighted average exercise price
Outstanding at January 1, 2012	$ 4.38
Canceled	$ 4.00
Outstanding at June 30, 2012	$ 4.59
Shares exercisable at June 30, 2012	$ 4.59