Net Income Per Share (Schedule Of Net Income Per Share To Shareholders) (Details) (USD $) In Thousands, except Per Share data	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Net Income Per Share [Abstract]
Net income to shareholders	$ 53,264	$ 63,250	$ 91,850	$ 126,650
Basic common shares outstanding	9,680	9,748	9,706	9,785
Dilutive potential common shares	38	12	40	10
Diluted shares outstanding	9,718	9,760	9,746	9,795
Basic net income per share	$ 5.50	$ 6.49	$ 9.46	$ 12.94
Diluted net income per share	$ 5.48	$ 6.48	$ 9.42	$ 12.93

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.

+ References+ Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

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-Appendix A

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-Glossary Other Comprehensive Income

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-Glossary Net Income

-URI http://asc.fasb.org/extlink&oid=6518256

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-Number 210

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+ Details

- 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.

+ References+ Details

- 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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-Glossary Weighted-Average Number of Common Shares Outstanding

-URI http://asc.fasb.org/extlink&oid=6528421

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+ Details