Shareholders' Equity - Reconciliation of Weighted Average Number of Shares (Detail) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Weighted Average Number of Shares Outstanding [Line Items]
Weighted average number of common shares outstanding	68,536	68,507	68,445	68,342
Director Plan and deferred stock units	233	338	287	348
ESOP	98	109	98	105
Common shares outstanding—basic	68,867	68,954	68,830	68,795
Common and potential common shares outstanding—diluted	70,755	71,161	70,759	70,993
Option plans and Omnibus Plan
Weighted Average Number of Shares Outstanding [Line Items]
Dilutive effect of Option Plans and Omnibus Plan	1,888	2,207	1,929	2,198

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.

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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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- 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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