Earnings Per Share - Summary of Earnings Per Share, Basic and Diluted (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Earnings Per Share Basic And Diluted By Common Class [Line Items]
Net income	$ 64,662	$ 42,079
Weighted-average shares outstanding	80,746	81,702
Share-based payment awards classified as participating securities	476	863
Denominator for basic earnings per share	81,222	82,565
Dilutive securities	2,738	2,599
Denominator for diluted earnings per share	83,960	85,164
Basic earnings per share	$ 0.80	$ 0.51
Diluted earnings per share	$ 0.77	$ 0.49
Earnings Per Share, Basic [Member]
Earnings Per Share Basic And Diluted By Common Class [Line Items]
Net income	$ 64,662	$ 42,079

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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- 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

This element represents nonvested share-based payment awards that contain non-forfeitable rights to dividends or dividend equivalents (whether paid or unpaid). Basic and dilutive earnings per share are generally disclosed for such shares using the two-class method.

+ References

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-Glossary Participating Security

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+ 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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-Glossary Other Comprehensive Income

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-Glossary Net Income

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-Appendix A

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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

This element represents the weighted average total number of shares issued throughout the period including the first (beginning balance outstanding) and last (ending balance outstanding) day of the period before considering any reductions (for instance, shares held in treasury) to arrive at the weighted average number of shares outstanding. Weighted average relates to the portion of time within a reporting period that common shares have been issued and outstanding to the total time in that period. Such concept is used in determining the weighted average number of shares outstanding for purposes of calculating earnings per share (basic).

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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.

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-Glossary Weighted-Average Number of Common Shares Outstanding

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

+ Details