Income Per Share of Common Stock (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income per share of common stock:
Net income for basic and diluted income per common share	$ 5,128	$ 4,262
Weighted-average shares for basic income per common share (in shares)	5,609	5,590
Effect of dilutive securities:
Employee and director stock options (in shares)	6	8
Adjusted weighted-average shares and assumed exercises for diluted income per common share (in shares)	5,615	5,598
Basic net income per common share (in dollars per share)	$ 0.91	$ 0.76
Diluted net income per common share (in dollars per share)	$ 0.91	$ 0.76
Options
Anti-dilutive securities
Anti-dilutive shares of common stock excluded from the calculation of dilutive securities	27	17