Income Per Share of Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income per share of common stock:
Net income for basic and diluted income per common share	$ 5,278	$ 3,687	$ 9,898	$ 7,753
Weighted-average shares for basic income per common share	5,578,000	5,565,000	5,576,000	5,571,000
Effect of dilutive securities:
Employee and director stock options (in shares)	10,000	3,000	10,000	3,000
Adjusted weighted-average shares and assumed exercises for diluted income per common share	5,588,000	5,568,000	5,586,000	5,574,000
Basic net income per common share (in dollars per share)	$ 0.95	$ 0.66	$ 1.77	$ 1.39
Diluted net income per common share (in dollars per share)	$ 0.94	$ 0.66	$ 1.77	$ 1.39
Options
Anti-dilutive securities
Anti-dilutive shares of common stock excluded from the calculation of dilutive securities		32,400		33,600