Information Regarding Shares of Common Stock Repurchased (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Equity, Class of Treasury Stock [Line Items]
Number of shares	3,025,700	4,040,000
Total cost	$ 207,918	$ 282,701	$ 434,656
Average cost per share	$ 68.72	$ 69.98