Net Income per Share (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Earnings Per Share [Abstract]
Net income	$ 9,564	$ 13,173
Less distributed and undistributed earnings allocated to participating securities	(282)	(383)
Net income allocated to common shares	$ 9,282	$ 12,790
Weighted average common shares outstanding (in shares)	24,823	24,897
Incremental shares from assumed conversions of common stock options (in shares)	7	30
Adjusted weighted average common shares outstanding (in shares)	24,830	24,927
Potentially dilutive securities not included in weighted average share calculation due to anti-dilutive effect (in shares)	0	16