Income Per Share of Common Stock (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Numerator:
Income for basic and diluted income per common share (in dollars)	$ 4,789	$ 3,947	$ 12,171	$ 12,631
Denominator:
Weighted-average shares for basic income per share	5,563,000	5,550,000	5,560,000	5,757,000
Effect of dilutive securities:
Employee and director stock options (in shares)	11,000	8,000	10,000	11,000
Adjusted weighted-average shares and assumed exercises for diluted income per share	5,574,000	5,558,000	5,570,000	5,768,000
Income per share of common stock:
Basic (in dollars per share)	$ 0.86	$ 0.71	$ 2.19	$ 2.19
Diluted (in dollars per share)	$ 0.86	$ 0.71	$ 2.19	$ 2.19
Options
Anti-dilutive securities
Anti-dilutive shares of common stock excluded from the calculation of dilutive securities	7,500	9,900	7,500	9,900