Income Per Share of Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Income per share of common stock:
Net income for basic and diluted income per common share	$ 4,620	$ 4,066
Weighted-average shares for basic income per share	5,576,000	5,577,000
Effect of dilutive securities:
Employee and director stock options (in shares)	9,000	3,000
Adjusted weighted-average shares and assumed exercises for diluted income per share	5,585,000	5,580,000
Basic net income per common share (in dollars per share)	$ 0.83	$ 0.73
Diluted net income per common share (in dollars per share)	$ 0.83	$ 0.73
Options
Anti-dilutive securities
Anti-dilutive shares of common stock excluded from the calculation of dilutive securities		35,000