Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Reconciliation of component parts of earnings per share [Abstract]
Net income	$ 10,714	$ 10,252	$ 33,533	$ 29,183
Less: Net income allocated to participating securities	12	11	38	33
Net income allocated to common shareholders	10,702	10,241	33,495	29,150
Basic EPS [Abstract]
Distributed earnings allocated to common stock	6,220	6,191	18,639	18,546
Undistributed earnings allocated to common stock	4,482	4,050	14,856	10,604
Net income allocated to common shareholders	10,702	10,241	33,495	29,150
Weighted average common shares outstanding including participating securities (in shares)	94,734,000	94,334,000	94,668,000	94,202,000
Less: Participating securities (in shares)	106,000	106,000	106,000	106,000
Weighted average common shares (in shares)	94,628,000	94,228,000	94,562,000	94,096,000
Basic EPS (in dollars per share)	$ 0.113	$ 0.109	$ 0.354	$ 0.310
Diluted EPS [Abstract]
Net income allocated to common shareholders	$ 10,702	$ 10,241	$ 33,495	$ 29,150
Weighted average common shares for basic EPS (in shares)	94,628,000	94,228,000	94,562,000	94,096,000
Effect of Dilutive Securities [Abstract]
Stock Options (in shares)	124,000	47,000	123,000	19,000
Weighted average common shares including potential dilutive shares (in shares)	94,752,000	94,275,000	94,685,000	94,115,000
Diluted EPS (in dollars per share)	$ 0.113	$ 0.109	$ 0.354	$ 0.310
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)	2,400,000	2,100,000	2,400,000	2,500,000