Net Income Per Common Share (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
Basic
Net income applicable to common stock	$ 7,037	$ 6,532	$ 19,356	$ 19,842
Average common shares outstanding	25,114,672	25,061,068	25,101,507	25,057,458
Net income per common share- basic	$ 0.28	$ 0.26	$ 0.77	$ 0.79
Diluted
Net income applicable to common stock	$ 7,037	$ 6,532	$ 19,356	$ 19,842
Average common shares outstanding	25,114,672	25,061,068	25,101,507	25,057,458
Effect of dilutive stock-based compensation	106,215	119,855	60,404	128,719
Average common shares outstanding - diluted	25,220,887	25,180,923	25,161,911	25,186,177
Net income per common share - diluted	$ 0.28	$ 0.26	$ 0.77	$ 0.79