Stock Option Activity Under Stock Option Plan (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Number of Shares
Beginning Balance	3,481,469
Granted	20,000	50,000
Exercised	(93,672)
Cancelled	(3,333)
Ending Balance	3,404,464		3,481,469
Vested and unvested expected to vest at end of period	3,337,935
Options exercisable, at end of period	2,122,328		2,120,834
Options available for future grant	2,751,563
Weighted Average Exercise Price
Beginning Balance	$ 4.96
Granted	5.66
Exercised	4.72
Cancelled	3.28
Ending Balance	4.97		$ 4.96
Vested and unvested expected to vest at end of period	4.29
Options exercisable, at end of period	$ 4.29		$ 4.24
Weighted Average Contractual Term (Years)
Outstanding, at end of period	6 years 9 months 7 days
Vested and unvested expected to vest at end of period	5 years 8 months 19 days
Options exercisable, at end of period	5 years 8 months 19 days		5 years 10 months 2 days
Aggregate Intrinsic Value
Outstanding, at end of period	$ 9,874
Vested and unvested expected to vest at end of period	9,681
Options exercisable, at end of period	$ 6,666		$ 8,622