Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Dilutive effect of stock options, restricted stock, and RSU awards for each period
Net Income	$ 9,573	$ 9,334	$ 28,856	$ 26,023
Weighted-average number of basic shares outstanding during the period	19,610	19,728	19,717	19,666
Dilutive effect of stock options, restricted stock and RSUs	160	132	287	222
Weighted-average number of diluted shares outstanding during the period	19,770	19,860	20,004	19,888
Basic earnings per share	$ 0.49	$ 0.47	$ 1.46	$ 1.32
Diluted earnings per share	$ 0.48	$ 0.47	$ 1.44	$ 1.31