Net Income per Share - Earnings Per Share (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Basic weighted average shares outstanding	4,889,772	4,878,986	4,886,258	4,874,565
Dilutive effect of granted options	5,020	11,064	7,729	18,777
Diluted weighted average shares outstanding	4,894,792	4,890,050	4,893,987	4,893,342
Net income	$ 1,688,140	$ 1,783,453	$ 3,460,527	$ 3,220,778
Net income per share-basic	$ 0.35	$ 0.37	$ 0.71	$ 0.66
Net income per share-diluted	$ 0.35	$ 0.36	$ 0.71	$ 0.66