Net Income Per Share - Components of Computation of Basic and Diluted Net Income Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator
Net income	$ 5,416	$ 1,968	$ 8,670	$ 4,953
Denominator
Weighted average common shares outstanding, basic	17,163	17,198	17,140	17,176
Options to purchase common stock	290	152	225	177
Restricted stock units	91	28	77	31
Employee stock purchase plan	5		4
Weighted average common shares outstanding, diluted	17,549	17,378	17,446	17,384
Net income per share
Basic	$ 0.32	$ 0.11	$ 0.51	$ 0.29
Diluted	$ 0.31	$ 0.11	$ 0.50	$ 0.29
Antidilutive shares (in thousands)	53	267	264	267