Income Per Share of Common Stock (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Income Per Share of Common Stock
Net income for basic and diluted income per common share	$ 5,718	$ 4,626	$ 10,210	$ 7,382
Weighted-average shares for basic income per share	5,578,000	5,560,000	5,577,000	5,559,000
Effect of dilutive securities:
Employee and director stock options (in shares)	11,000	9,000	11,000	9,000
Adjusted weighted-average shares and assumed exercises for diluted income per share	5,589,000	5,569,000	5,588,000	5,568,000
Basic net income per common share (in dollars per share)	$ 1.03	$ 0.83	$ 1.83	$ 1.33
Diluted net income per common share (in dollars per share)	$ 1.02	$ 0.83	$ 1.83	$ 1.33
Employee and Nonemployee Stock Option [Member]
Anti-dilutive securities
Anti-dilutive shares of common stock excluded from the calculation of dilutive securities	15,000	9,900	15,000	9,900