Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Reconciliation of component parts of earnings per share [Abstract]
Net income	$ 10,727	$ 11,808	$ 21,442	$ 22,819
Less: Net income allocated to participating securities	0	13	0	26
Net income allocated to common shareholders	10,727	11,795	21,442	22,793
Basic EPS [Abstract]
Distributed earnings allocated to common stock	6,238	6,213	12,466	12,419
Undistributed earnings allocated to common stock	4,489	5,582	8,976	10,374
Net income allocated to common shareholders	$ 10,727	$ 11,795	$ 21,442	$ 22,793
Weighted average common shares outstanding including participating securities (in shares)	95,056	94,665	95,002	94,642
Less: Participating securities (in shares)	0	106	0	106
Weighted average common shares (in shares)	95,056	94,559	95,002	94,536
Basic EPS (in dollars per share)	$ 0.113	$ 0.125	$ 0.226	$ 0.241
Diluted EPS [Abstract]
Net income allocated to common shareholders	$ 10,727	$ 11,795	$ 21,442	$ 22,793
Weighted average common shares for basic EPS (in shares)	95,056	94,559	95,002	94,536
Effect of Dilutive Securities [Abstract]
Stock Options (in shares)	134	116	130	122
Weighted average common shares including potential dilutive shares (in shares)	95,190	94,675	95,132	94,658
Diluted EPS (in dollars per share)	$ 0.113	$ 0.125	$ 0.225	$ 0.241
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of antidilutive stock options excluded from diluted earnings per share (in shares)	1,400	2,400	1,400	2,400