Stock Option Activity Under Stock Option Plan (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Number of Shares
Beginning Balance			5,138,486
Granted	361,900	516,000	425,400	1,063,900
Exercised			(8,300)
Cancelled			(158,432)
Ending Balance	5,397,154		5,397,154
Vested and unvested expected to vest at end of period	5,340,550		5,340,550
Options exercisable, at end of period	3,124,387		3,124,387
Options exercisable, at beginning of period			2,911,186
Options available for future grant	3,678,000		3,678,000
Weighted Average Exercise Price
Beginning Balance			$ 4.08
Granted			$ 4.96
Exercised			$ 3.61
Cancelled			$ 5.90
Ending Balance	$ 4.10		$ 4.10
Vested and unvested expected to vest at end of period	$ 4.10		$ 4.10
Options exercisable, at end of period	$ 3.40		$ 3.40
Options exercisable, at beginning of period			$ 3.21
Outstanding, at end of period (in years)			7 years 2 months 9 days
Vested and unvested expected to vest at end of period (in years)			7 years 2 months 9 days
Aggregate Intrinsic Value
Outstanding, at end of period			$ 10,320
Vested and unvested expected to vest at end of period	10,212		10,212
Options exercisable, at end of period	8,137		8,137
Options exercisable, at beginning of period			$ 4,232
End of Period
Weighted Average Exercise Price
Options exercisable			5 years 3 months 11 days
Beginning of Period
Weighted Average Exercise Price
Options exercisable			5 years 6 months 7 days