Income Per Share of Common Stock (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Numerator:
Income for basic and diluted income per common share (in dollars)	$ 3,947	$ 7,062	$ 12,631	$ 17,671
Denominator:
Weighted-average shares for basic income per share	5,550,000	6,322,000	5,757,000	6,384,000
Effect of dilutive securities:
Employee and director stock options	8,000	16,000	11,000	17,000
Adjusted weighted-average shares and assumed exercises for diluted income per share	5,558,000	6,338,000	5,768,000	6,401,000
Income per share of common stock:
Basic (in dollars per share)	$ 0.71	$ 1.12	$ 2.19	$ 2.77
Diluted (in dollars per share)	$ 0.71	$ 1.11	$ 2.19	$ 2.76
Options
Anti-dilutive securities
Anti-dilutive shares of common stock excluded from the calculation of dilutive securities	9,900	9,500	9,900	9,500