Summary of Activity under Stock-Based Compensation Plans (Detail) (USD $)	6 Months Ended	12 Months Ended
	Jun. 30, 2012	Dec. 31, 2011
Shares Available for Grant
Beginning Balance	10,114,332	7,542,277
Authorized		4,000,000
Granted	(1,467,745)	(1,447,980)
Cancelled or Expired	59,626	20,035
Ending Balance	8,706,213	10,114,332
Stock Options Number Outstanding
Beginning Balance	2,266,822	1,810,188
Granted	1,286,110	820,716
Cancelled or Expired	(282,985)	(343,081)
Exercised		(21,001)
Ending Balance	3,269,947	2,266,822
Vested or expected to vest at June 30, 2012	3,121,589
Stock Options Average Exercise Price per share
Beginning Balance	$ 2.86	$ 3.56
Granted	$ 1.33	$ 2.53
Cancelled or Expired	$ 2.79	$ 7.27
Exercised		$ 2.36
Ending Balance	$ 2.26	$ 2.86
Vested or expected to vest at June 30, 2012	$ 2.29
Stock Options Aggregate Intrinsic Value
Beginning Balance	$ 49,298	$ 128,300
Ending Balance		49,298
Vested or expected to vest at June 30, 2012
Remaining Contractual Life(in years)
Beginning Balance	5 years 10 months 24 days	4 years 7 months 28 days
Ending Balance	7 years 29 days	5 years 10 months 24 days
Vested or expected to vest at June 30, 2012	6 years 11 months 23 days
Stock Awards Number Granted
Granted	181,635	627,264
Stock Awards Fair Value
Granted	$ 272,655	$ 1,627,969