Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Reconciliation of component parts of earnings per share [Abstract]
Net income	$ 11,011	$ 9,168
Less: Net income allocated to participating securities	12	10
Net income allocated to common shareholders	10,999	9,158
Basic EPS [Abstract]
Distributed earnings allocated to common stock	6,206	6,173
Undistributed earnings allocated to common stock	4,793	2,985
Net income allocated to common shareholders	10,999	9,158
Weighted average common shares outstanding including participating securities (in shares)	94,558,000	94,068,000
Less: Participating securities (in shares)	106,000	106,000
Weighted average common shares (in shares)	94,452,000	93,962,000
Basic EPS (in dollars per share)	$ 0.116	$ 0.097
Diluted EPS [Abstract]
Net income allocated to common shareholders	$ 10,999	$ 9,158
Weighted average common shares for basic EPS (in shares)	94,452,000	93,962,000
Effect of Dilutive Securities [Abstract]
Stock Options (in shares)	129,000	5,000
Weighted average common shares including potential dilutive shares (in shares)	94,581,000	93,967,000
Diluted EPS (in dollars per share)	$ 0.116	$ 0.097
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	2,700,000