Income Per Share of Common Stock (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Income per share of common stock:
Net income for basic and diluted income per common share	$ 5,544	$ 5,128
Weighted-average shares for basic income per common share (in shares)	5,624	5,609
Effect of dilutive securities:
Employee and director stock options (in shares)	10	6
Adjusted weighted-average shares and assumed exercises for diluted income per common share (in shares)	5,634	5,615
Basic net income per common share (in dollars per share)	$ 0.99	$ 0.91
Diluted net income per common share (in dollars per share)	$ 0.98	$ 0.91
Options
Anti-dilutive securities
Anti-dilutive shares of common stock excluded from the calculation of dilutive securities	8	27