Stock Option Activity Under Stock Option Plan (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Number of Shares
Beginning Balance	3,465,335
Granted	117,000
Exercised	(5,000)
Cancelled	(37,666)
Ending Balance	3,539,669	3,465,335
Options exercisable, at end of period	2,673,668	2,671,835
Options available for future grant	1,698,426
Weighted Average Exercise Price
Beginning Balance	$ 5.07
Granted	6.42
Exercised	4.89
Cancelled	6.25
Ending Balance	5.10	$ 5.07
Options exercisable, at end of period	$ 4.41	$ 4.40
Weighted Average Contractual Term (Years)
Outstanding, at end of period	6 years 6 months 18 days
Options exercisable, at end of period	5 years 7 months 17 days	5 years 10 months 17 days
Aggregate Intrinsic Value
Outstanding, at end of period	$ 6,295
Options exercisable, at end of period	$ 5,795	$ 3,383