Earnings Per Share Earnings Per Share - Reconciliation (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Earnings Per Share [Abstract]
Numerator for basic and diluted EPS — net income allocated to common stockholders	$ 13,618	$ 16,136
Denominator for basic EPS — weighted average number of shares (shares)	30,171,840	30,522,767
Add — dilutive effect of:
Weighted average number of incremental shares issuable from restricted stock units (shares)	89,000	9,000
Denominator for diluted EPS — weighted average number of shares and dilutive potential shares (shares)	30,260,963	30,532,162
Earnings per share:
Basic (usd per share)	$ 0.45	$ 0.53
Diluted (usd per share)	$ 0.45	$ 0.53

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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+ Details

- Definition

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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- Definition

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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- Definition

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.

+ References

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Reference 7: http://www.xbrl.org/2003/role/presentationRef

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-Glossary Weighted-Average Number of Common Shares Outstanding

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