Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Basic and Diluted Earnings Per Share
Net income available to common stockholders, basic and diluted	$ 27,670us-gaap_NetIncomeLoss	$ 26,730us-gaap_NetIncomeLoss
Average outstanding shares - basic	75,206,348	74,437,393
Add: dilutive stock options and awards	38,611	43,425
Average outstanding shares - diluted	75,244,959	74,480,818
Basic earnings per share	$ 0.37us-gaap_EarningsPerShareBasic	$ 0.36us-gaap_EarningsPerShareBasic
Diluted earnings per share	$ 0.37us-gaap_EarningsPerShareDiluted	$ 0.36us-gaap_EarningsPerShareDiluted
Earnings Per Share
Stock options and restricted stock awards excluded from the diluted average outstanding share calculation	55,497	0

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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