Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Basic and Diluted Earnings Per Share
Net income available to common stockholders, basic and diluted	$ 33,687	$ 30,451	$ 64,942	$ 59,133
Average outstanding shares - basic	77,546,236	76,170,734	77,061,867	76,148,493
Add: dilutive restricted stock awards	46,089	34,335	63,810	43,162
Average outstanding shares - diluted	77,592,325	76,205,069	77,125,677	76,191,655
Basic earnings per share	$ 0.43	$ 0.40	$ 0.84	$ 0.78
Diluted earnings per share	$ 0.43	$ 0.40	$ 0.84	$ 0.78
Earnings Per Share
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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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units 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 portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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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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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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