Income Per Share of Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income per share of common stock:
Net income for basic and diluted income per common share	$ 6,081	$ 5,676	$ 13,834	$ 10,600
Weighted-average shares for basic income per share	5,565,000	5,600,000	5,569,000	5,599,000
Effect of dilutive securities:
Employee and director stock options (in shares)	4,000	4,000	3,000	6,000
Adjusted weighted-average shares and assumed exercises for diluted income per share	5,569,000	5,604,000	5,572,000	5,605,000
Basic net income per common share (in dollars per share)	$ 1.09	$ 1.01	$ 2.48	$ 1.89
Diluted net income per common share (in dollars per share)	$ 1.09	$ 1.01	$ 2.48	$ 1.89
Options
Anti-dilutive securities
Anti-dilutive shares of common stock excluded from the calculation of dilutive securities	7,500	34,800	7,500	17,400