Summary of Significant Accounting Policies (Details 3) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Summary of Significant Accounting Policies
Net income for basic and diluted income per common share	$ 2,629	$ 4,789	$ 4,626	$ 2,757	$ 3,792	$ 3,947	$ 4,060	$ 4,624	$ 14,800	$ 16,423	$ 22,186
Weighted-average shares for basic income per share									5,561,429	5,705,475	6,343,992
Effect of dilutive securities:
Employee and director stock options (in shares)									9,850	10,286	18,449
Adjusted weighted-average shares and assumed exercises for diluted income per share									5,571,279	5,715,761	6,362,441
Basic net income per common share (in dollars per share)	$ 0.47	$ 0.86	$ 0.83	$ 0.50	$ 0.68	$ 0.71	$ 0.73	$ 0.75	$ 2.66	$ 2.88	$ 3.50
Diluted net income per common share (in dollars per share)	$ 0.47	$ 0.86	$ 0.83	$ 0.50	$ 0.68	$ 0.71	$ 0.73	$ 0.75	$ 2.66	$ 2.87	$ 3.49
Options
Anti-dilutive securities
Anti-dilutive shares of common stock excluded from the calculation of dilutive securities									15,000	17,400	7,500