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Shareholders' Equity - Additional Information (Detail)	12 Months Ended
Shareholders' Equity - Additional Information (Detail)	Dec. 31, 2011	Dec. 31, 2010
Class of Stock [Line Items]
Treasury Shares	15,111,635	10,664,728
Additional authorized shares purchased	5,281,344
Preferred stock, authorized	1,000,000
Nonvoting Common Stock
Class of Stock [Line Items]
Nonvoting common stock repurchased	5,075,675	1,478,805

Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

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