Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Reconciliation of component parts of earnings per share [Abstract]
Net income	$ 10,616	$ 10,714	$ 32,058	$ 33,533
Less: Net income allocated to participating securities	0	12	0	38
Net income allocated to common shareholders	10,616	10,702	32,058	33,495
Basic EPS [Abstract]
Distributed earnings allocated to common stock	6,244	6,220	18,710	18,639
Undistributed earnings allocated to common stock	4,372	4,482	13,348	14,856
Net income allocated to common shareholders	$ 10,616	$ 10,702	$ 32,058	$ 33,495
Weighted average common shares outstanding including participating securities (in shares)	95,149	94,734	95,051	94,668
Less: Participating securities (in shares)	0	106	0	106
Weighted average common shares (in shares)	95,149	94,628	95,051	94,562
Basic EPS (in dollars per share)	$ 0.112	$ 0.113	$ 0.337	$ 0.354
Diluted EPS [Abstract]
Net income allocated to common shareholders	$ 10,616	$ 10,702	$ 32,058	$ 33,495
Weighted average common shares for basic EPS (in shares)	95,149	94,628	95,051	94,562
Effect of Dilutive Securities [Abstract]
Stock Options (in shares)	85	124	116	123
Weighted average common shares including potential dilutive shares (in shares)	95,234	94,752	95,167	94,685
Diluted EPS (in dollars per share)	$ 0.111	$ 0.113	$ 0.337	$ 0.354
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