Stock Option Activity Under Stock Option Plan (Detail) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares
Number of Shares
Beginning Balance	3,465,335
Granted	359,000
Exercised	(80,000)
Cancelled	(122,000)
Ending Balance	3,622,335	3,465,335
Options exercisable, at end of period	2,696,835	2,671,835
Options available for future grant	1,540,760
Weighted Average Exercise Price
Beginning Balance | $ / shares	$ 5.07
Granted | $ / shares	6.28
Exercised | $ / shares	4.85
Cancelled | $ / shares	6.64
Ending Balance | $ / shares	5.14	$ 5.07
Options exercisable, at end of period | $ / shares	$ 4.62	$ 4.40
Weighted Average Contractual Term (Years)
Outstanding, at end of period	6 years 2 months 19 days
Options exercisable, at end of period	5 years 4 months 20 days	5 years 10 months 17 days
Aggregate Intrinsic Value
Outstanding, at end of period | $	$ 5,657
Options exercisable, at end of period | $	$ 5,215	$ 3,383