Income Per Share of Common Stock (Details) - 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
Income per share of common stock:
Net income for basic and diluted income per common share	$ 6,638	$ 5,278	$ 10,900	$ 9,898
Weighted-average shares for basic income per common share	5,595	5,578	5,593	5,576
Effect of dilutive securities:
Employee and director stock options (in shares)	8	10	8	10
Adjusted weighted-average shares and assumed exercises for diluted income per common share	5,603	5,588	5,601	5,586
Basic net income per common share (in dollars per share)	$ 1.19	$ 0.95	$ 1.95	$ 1.77
Diluted net income per common share (in dollars per share)	$ 1.18	$ 0.94	$ 1.95	$ 1.77
Options
Anti-dilutive securities
Anti-dilutive shares of common stock excluded from the calculation of dilutive securities	2		10