Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Basic and Diluted Earnings Per Share
Net income available to common stockholders, basic and diluted	$ 30,451	$ 29,335	$ 59,133	$ 57,005
Average outstanding shares - basic	76,170,734	75,530,591	76,148,493	75,369,366
Add: dilutive stock options and awards	34,335	35,064	43,162	38,255
Average outstanding shares - diluted	76,205,069	75,565,655	76,191,655	75,407,621
Basic earnings per share	$ 0.40	$ 0.39	$ 0.78	$ 0.76
Diluted earnings per share	$ 0.40	$ 0.39	$ 0.78	$ 0.76
Earnings Per Share
Stock options and restricted stock awards excluded from the diluted average outstanding share calculation			0	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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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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