Income Per Share of Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Per Share of Common Stock
Net income for basic and diluted income per common share	$ 5,676	$ 5,426	$ 10,600	$ 15,636
Weighted-average shares for basic income per share	5,600,000	5,578,000	5,599,000	5,578,000
Effect of dilutive securities:
Employee and director stock options (in shares)	4,000	11,000	6,000	10,000
Adjusted weighted-average shares and assumed exercises for diluted income per share	5,604,000	5,589,000	5,605,000	5,588,000
Basic net income per common share (in dollars per share)	$ 1.01	$ 0.97	$ 1.89	$ 2.80
Diluted net income per common share (in dollars per share)	$ 1.01	$ 0.97	$ 1.89	$ 2.80
Options
Anti-dilutive securities
Anti-dilutive shares of common stock excluded from the calculation of dilutive securities			35,000	15,000