Stock Compensation - Summary of Option Activity in 2015 Plan, 2007 Plan and 1999 Plan (Detail) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares, Outstanding at beginning of year | shares	223,432
Shares, Exercised | shares	(33,000)
Shares, Outstanding at end of period | shares	190,432
Shares, Shares subject to options exercisable at end of period | shares	190,432
Weighted average exercise price, Outstanding at beginning of year | $ / shares	$ 3.93
Weighted average exercise price, Exercised | $ / shares	2.10
Weighted average exercise price, Outstanding at end of period | $ / shares	4.25
Weighted average exercise price, Shares subject to options exercisable at end of period | $ / shares	$ 4.25
Aggregate intrinsic value, Outstanding at end of period | $	$ 986
Aggregate intrinsic value, Shares subject to options exercisable at end of period | $	$ 986