Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Reconciliation of component parts of earnings per share [Abstract]
Net income	$ 11,808	$ 9,763	$ 22,819	$ 18,931
Less: Net income allocated to participating securities	13	11	26	21
Net income allocated to common shareholders	11,795	9,752	22,793	18,910
Basic EPS [Abstract]
Distributed earnings allocated to common stock	6,213	6,182	12,419	12,356
Undistributed earnings allocated to common stock	5,582	3,570	10,374	6,554
Net income allocated to common shareholders	11,795	9,752	22,793	18,910
Weighted average common shares outstanding including participating securities (in shares)	94,665,000	94,204,000	94,642,000	94,134,000
Less: Participating securities (in shares)	106,000	106,000	106,000	106,000
Weighted average common shares (in shares)	94,559,000	94,098,000	94,536,000	94,028,000
Basic EPS (in dollars per share)	$ 0.125	$ 0.104	$ 0.241	$ 0.201
Diluted EPS [Abstract]
Net income allocated to common shareholders	$ 11,795	$ 9,752	$ 22,793	$ 18,910
Weighted average common shares for basic EPS (in shares)	94,559,000	94,098,000	94,536,000	94,028,000
Effect of Dilutive Securities [Abstract]
Stock Options (in shares)	116,000	7,000	122,000	6,000
Weighted average common shares including potential dilutive shares (in shares)	94,675,000	94,105,000	94,658,000	94,034,000
Diluted EPS (in dollars per share)	$ 0.125	$ 0.104	$ 0.241	$ 0.201
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	2,400,000	2,700,000