Schedule of Basic and Diluted Earnings Per Share (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 [Line Items]
Basic earnings per share, Weighted Average Shares	41,742	41,653
Potential dilutive effect of stock options outstanding, Weighted Average Shares	97	112
Diluted earnings per share, Weighted Average Shares	41,839	41,765
Basic earnings per share, Earnings per Share	$ 1.11	$ 0.98
Potential dilutive effect of stock options outstanding, Earnings per Share	$ 0.00	$ 0.00
Diluted earnings per share, Earnings Per Share	$ 1.11	$ 0.98

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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- Definition

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic net Income or Loss per outstanding limited partnership unit in the future and that were not included in the computation of diluted net income per limited partnership unit, because to do so would increase net income per unit amounts or decrease loss per unit amounts for the period presented.

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- Definition

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 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.

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