Stock Option Activity Under Stock Option Plan (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Number of Shares
Beginning Balance			6,747,302
Granted	23,800	1,315,500	104,300	1,426,400
Exercised			(583,038)
Cancelled			(227,402)
Ending Balance	6,041,162		6,041,162		6,747,302
Vested and unvested expected to vest at end of period	5,988,240		5,988,240
Options exercisable, at end of period	3,176,594		3,176,594		3,471,935
Options available for future grant	5,317,831		5,317,831
Weighted Average Exercise Price
Beginning Balance			$ 3.81
Granted			$ 3.54
Exercised			$ 2.26
Cancelled			$ 5.05
Ending Balance	$ 3.91		$ 3.91		$ 3.81
Vested and unvested expected to vest at end of period	$ 4.11		$ 4.11
Options exercisable, at end of period	$ 4.11		$ 4.11		$ 4.01
Weighted Average Contractual Term (Years)
Outstanding, at end of period			7 years 2 months 27 days
Vested and unvested expected to vest at end of period			5 years 7 months 10 days
Options exercisable, at end of period			5 years 7 months 10 days		5 years 11 days
Aggregate Intrinsic Value
Outstanding, at end of period	$ 4,456		$ 4,456
Vested and unvested expected to vest at end of period	4,417		4,417
Options exercisable, at end of period	$ 1,846		$ 1,846		$ 2,654