Net Income per Share (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share [Abstract]
Net income	$ 8,385	$ 10,082	$ 19,840	$ 26,743
Less distributed and undistributed earnings allocated to participating securities	(243)	(289)	(576)	(769)
Net income allocated to common shares	$ 8,142	$ 9,793	$ 19,264	$ 25,974
Weighted average common shares outstanding (in shares)	24,650	24,849	24,747	24,855
Incremental shares from assumed conversions of common stock options (in shares)	2	18	5	24
Adjusted weighted average common shares outstanding (in shares)	24,652	24,867	24,752	24,879
Potentially dilutive securities not included in weighted average share calculation due to anti-dilutive effect (in shares)	16	0	5	10