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, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Number of Shares
Beginning Balance			6,747,302
Granted	10,000	125,000	114,300	1,551,400
Exercised			(585,638)
Cancelled			(483,536)
Ending Balance	5,792,428		5,792,428		6,747,302
Vested and unvested expected to vest at end of period	5,731,490		5,731,490
Options exercisable, at end of period	3,257,661		3,257,661		3,471,935
Options available for future grant	5,555,864		5,555,864
Weighted Average Exercise Price
Beginning Balance			$ 3.81
Granted			$ 4.11
Exercised			$ 2.26
Cancelled			$ 4.28
Ending Balance	$ 3.94		$ 3.94		$ 3.81
Vested and unvested expected to vest at end of period	$ 4.12		$ 4.12
Options exercisable, at end of period	$ 4.12		$ 4.12		$ 4.01
Weighted Average Contractual Term (Years)
Outstanding, at end of period			6 years 10 months 28 days
Vested and unvested expected to vest at end of period			5 years 4 months 28 days
Options exercisable, at end of period			5 years 4 months 28 days		5 years 11 days
Aggregate Intrinsic Value
Outstanding, at end of period	$ 1,457		$ 1,457
Vested and unvested expected to vest at end of period	1,441		1,441
Options exercisable, at end of period	$ 498		$ 498		$ 2,654