Net Income Per Share (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Net Income Per Share [Abstract]
Net income	$ 5,621	$ 6,741	$ 19,505	$ 15,527
Less income allocated to participating securities	(162)	(199)	(564)	(463)
Net income allocated to common shares	$ 5,459	$ 6,542	$ 18,941	$ 15,064
Weighted average common shares outstanding (in shares)	25,095	25,726	25,091	25,608
Incremental shares from assumed conversions of common stock options (in shares)	60	101	66	110
Adjusted weighted average common shares outstanding (in shares)	25,155	25,827	25,157	25,718
Potentially dilutive securities not included in weighted average share calculation due to anti-dilutive effect (in shares)	42	8	29	4