Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Basic earnings per common share
Net income	$ 8,972	$ 9,723	$ 4,705	$ 8,923
Less income allocated to participating securities	94	114	32	110
Net income attributable to common shareholders	8,878	9,609	4,673	8,813
Weighted average common shares outstanding	21,906,622	21,661,662	21,866,662	21,536,441
Basic earnings per common share (in dollars per share)	$ 0.41	$ 0.44	$ 0.21	$ 0.41
Earnings per common share assuming dilution
Net income	8,972	9,723	4,705	8,923
Less income allocated to participating securities	94	114	32	110
Net income attributable to common shareholders	$ 8,878	$ 9,609	$ 4,673	$ 8,813
Weighted average common shares outstanding	21,906,622	21,661,662	21,866,662	21,536,441
Incremental shares applicable to stock based compensation	55,476	106,723	119,312	131,103
Weighted average common shares assuming dilution	21,962,098	21,768,385	21,985,974	21,667,544
Earnings per common share assuming dilution (in dollars per share)	$ 0.40	$ 0.44	$ 0.21	$ 0.41