Reconciliation of Weighted Average Number Shares (Detail) In Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Weighted Average Number of Shares Outstanding [Line Items]
Weighted average number of common shares outstanding	68,449	66,251	68,284	65,886
Director Plan and Deferred stock units	349	313	339	328
ESOP	139	247	138	273
Common shares outstanding - basic	68,937	66,811	68,761	66,487
Common and potential common shares outstanding - diluted	71,289	68,753	71,056	68,250
Restricted Plan And Omnibus Plan Member
Weighted Average Number of Shares Outstanding [Line Items]
Dilutive effect	186	135	178	127
Option Plans And Omnibus Plan Member
Weighted Average Number of Shares Outstanding [Line Items]
Dilutive effect	2,166	1,807	2,117	1,636

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.

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).

+ References

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

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+ 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

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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+ Details