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Schedule of Information Related To Stock Repurchase Programs (Parenthetical) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Tax Withholding Obligations
Class of Stock [Line Items]
Number of shares repurchased	432,562	217,649	293,933
Shares repurchased at an average price	$ 44.28	$ 45.51	$ 39.22
Restricted Stock
Class of Stock [Line Items]
Number of shares repurchased	750		8,000
Shares repurchased at an average price	$ 0.01		$ 0.01

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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