Stock Option Activity Under Stock Option Plan (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Number of Shares
Beginning Balance			7,147,303
Granted	125,000	76,300	1,551,400	508,700
Exercised			(570,168)
Cancelled			(2,398,366)
Ending Balance	5,730,169		5,730,169		7,147,303
Vested and unvested expected to vest at end of period	5,675,997		5,675,997
Options exercisable, at end of period	2,996,068		2,996,068		3,683,786
Options available for future grant	1,565,070		1,565,070
Weighted Average Exercise Price
Beginning Balance			$ 4.11
Granted			$ 2.55
Exercised			$ 1.68
Cancelled			$ 4.57
Ending Balance	$ 3.73		$ 3.73		$ 4.11
Vested and unvested expected to vest at end of period	$ 3.95		$ 3.95
Options exercisable, at end of period	$ 3.95		$ 3.95		$ 3.56
Weighted Average Contractual Term (Years)
Outstanding, at end of period			6 years 10 months 21 days
Vested and unvested expected to vest at end of period			4 years 9 months
Options exercisable, at end of period			4 years 9 months		5 years 3 months 11 days
Aggregate Intrinsic Value
Outstanding, at end of period	$ 4,255		$ 4,255
Vested and unvested expected to vest at end of period	4,215		4,215
Options exercisable, at end of period	$ 2,203		$ 2,203		$ 3,972