Shares of Common Stock Repurchased (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011
Equity, Class of Treasury Stock [Line Items]
Number of shares	928,500	1,100,000	3,025,700		3,100,000
Total cost	$ 61,261	$ 79,423	$ 207,918	$ 64,181	$ 218,520
Average cost per share	$ 65.98	$ 72.20	$ 68.72		$ 70.49