Earnings per Common Share - Computation of Basic and Diluted Earnings per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Numerator [Abstract]
Net income	$ 6,448	$ 5,907
Denominator [Abstract]
Weighted average shares outstanding - basic (in shares)	4,941,233	4,924,636
Potentially dilutive common shares - restricted stock units (in shares)	2,665	3,548
Weighted average shares outstanding - diluted (in shares)	4,943,898	4,928,184
Basic (in usd per share)	$ 1.30	$ 1.20
Diluted (in usd per share)	$ 1.30	$ 1.20