Earnings Per Share (Details) (USD $) In Thousands, except Per Share data	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Earnings:
Net income (numerator for basic and diluted calculations)	$ 132,888	$ 127,019	$ 293,704	$ 249,458
Shares:
Weighted average outstanding shares (denominator for basic calculation)	73,971	73,141	73,593	73,094
Denominator for diluted calculation	74,530	74,721	74,184	74,650
Earnings Per Share:
Basic earning per share	$ 1.80	$ 1.74	$ 3.99	$ 3.41
Diluted earnings per share	$ 1.78	$ 1.70	$ 3.96	$ 3.34

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- Definition

The amount of net income or loss for the period per each share of common stock outstanding during the reporting period.

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- Definition

The amount of net income or loss for the period per each share of common stock and dilutive common stock equivalents outstanding during the reporting period.

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- Definition

The portion of consolidated profit or loss for the period, net of income taxes, which is attributable to the parent. If the entity does not present consolidated financial statements, the amount of profit or loss for the period, net of income taxes.

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The average number of shares issued and outstanding that are used in calculating diluted EPS, determined based on the timing of issuance of shares in the period.

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

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