Net Income Per Share (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Net Income Per Share [Abstract]
Net income	$ 11,452	$ 4,099	$ 30,957	$ 19,626
Less income allocated to participating securities	(334)	(120)	(898)	(582)
Net income allocated to common shares	$ 11,118	$ 3,979	$ 30,059	$ 19,044
Weighted average common shares outstanding (in shares)	24,923	25,425	25,034	25,546
Incremental shares from assumed conversions of common stock options (in shares)	57	74	63	98
Adjusted weighted average common shares outstanding (in shares)	24,980	25,499	25,097	25,644
Potentially dilutive securities not included in weighted average share calculation due to anti-dilutive effect (in shares)	41	54	33	21