Income Per Share of Common Stock (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2012 Options	Dec. 31, 2011 Options
Numerator:
Income for basic and diluted income per common share	$ 4,060	$ 5,795	$ 8,684	$ 10,609
Denominator:
Weighted-average shares for basic income per share	5,550,000	6,417,000	5,861,000	6,415,000
Effect of dilutive securities:
Employee and director stock options (in shares)	9,000	16,000	12,000	17,000
Adjusted weighted-average shares and assumed exercises for diluted income per share	5,559,000	6,433,000	5,873,000	6,432,000
Income per share of common stock:
Basic (in dollars per share)	$ 0.73	$ 0.90	$ 1.48	$ 1.65
Diluted (in dollars per share)	$ 0.73	$ 0.90	$ 1.48	$ 1.65
Anti-dilutive securities
Anti-dilutive shares of common stock excluded from the calculation of dilutive securities					10,000	10,000