Earnings Per Share (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012
Computation of Earnings per Share
Net income	$ 8,477	$ 4,722	$ 5,020	$ 5,321	$ 3,931
Average number of common shares outstanding	16,002				15,979
Effect of dilutive stock options	89				64
Average number of common shares outstanding used to calculate diluted earnings per share	16,091				16,043
Options excluded from diluted earnings per share because the effect of these options was antidilutive	856				869