Stock Option Activity Under Stock Option Plan (Detail) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Number of Shares
Beginning Balance	3,481,469
Granted	157,300
Exercised	(169,000)
Cancelled	(21,699)
Ending Balance	3,448,070	3,481,469
Vested and unvested expected to vest at end of period	3,357,976
Options exercisable, at end of period	2,317,935	2,120,834
Options available for future grant	2,632,629
Weighted Average Exercise Price
Beginning Balance	$ 4.96
Granted	7.76
Exercised	4.81
Cancelled	6.18
Ending Balance	5.08	$ 4.96
Vested and unvested expected to vest at end of period	4.25
Options exercisable, at end of period	$ 4.25	$ 4.24
Weighted Average Contractual Term (Years)
Outstanding, at end of period	6 years 6 months 7 days
Vested and unvested expected to vest at end of period	5 years 6 months 26 days
Options exercisable, at end of period	5 years 6 months 26 days	5 years 10 months 2 days
Aggregate Intrinsic Value
Outstanding, at end of period	$ 4,319
Vested and unvested expected to vest at end of period	4,206
Options exercisable, at end of period	$ 3,755	$ 8,622