Stock Option Activity Under Stock Option Plan (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Number of Shares
Beginning Balance			5,138,486
Granted	76,300	509,000	508,700	1,600,000
Exercise			(8,300)
Cancelled			(277,399)
Ending Balance	5,361,487		5,361,487
Vested and unvested expected to vest at end of period	5,262,835		5,262,835
Options exercisable, at end of period	3,301,387		3,301,387
Options exercisable, at beginning of period			2,911,186
Options available for future grant	3,594,700		3,594,700
Weighted Average Exercise Price
Beginning Balance			$ 4.08
Granted			$ 5.07
Exercised			$ 3.61
Cancelled			$ 5.67
Ending Balance	$ 4.09		$ 4.09
Vested and unvested expected to vest at end of period	$ 4.09		$ 4.09
Options exercisable, at end of period	$ 3.50		$ 3.50
Options exercisable, at beginning of period			$ 3.21
Options exercisable			6 years 10 months 17 days
Vested and unvested expected to vest at end of period (in years)			6 years 10 months 17 days
Aggregate Intrinsic Value
Outstanding, at end of period			$ 8,037
Vested and unvested expected to vest at end of period	7,889		7,889
Options exercisable, at end of period	6,764		6,764
Options exercisable, at beginning of period			$ 4,232
End of Period [Member]
Weighted Average Exercise Price
Options exercisable			5 years 2 months 23 days
Beginning of Period [Member]
Weighted Average Exercise Price
Options exercisable			5 years 6 months 7 days