Share Repurchase Activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011
Stockholders Equity Note [Line Items]
Number of shares repurchased	1,979,429	[1]	1,410,828	[1]
Cost of repurchased shares (in thousands)	$ 77,158		$ 51,896

[1] The average purchase price for the shares was $38.98 in 2012 and $36.78 in 2011.