Income Per Share of Common Stock (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income per share of common stock:
Net income for basic and diluted income per common share	$ 4,554	$ 5,667	$ 15,454	$ 15,565
Weighted-average shares for basic income per common share	5,598	5,577	5,595	5,577
Effect of dilutive securities:
Employee and director stock options (in shares)	8	10	7	9
Adjusted weighted-average shares and assumed exercises for diluted income per common share	5,606	5,587	5,602	5,586
Basic net income per common share (in dollars per share)	$ 0.81	$ 1.02	$ 2.76	$ 2.79
Diluted net income per common share (in dollars per share)	$ 0.81	$ 1.01	$ 2.76	$ 2.79
Options
Anti-dilutive securities
Anti-dilutive shares of common stock excluded from the calculation of dilutive securities	2		7