Share Repurchase Activity (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		Jun. 30, 2011
Stockholders Equity Note [Line Items]
Number of shares repurchased	184,831	[1]	932,624	[1]	2,164,260	[1]	2,343,452	[1]
Cost of repurchased shares (in thousands)	$ 7,517		$ 35,964		$ 84,674		$ 87,860

[1] The average purchase price for the shares was $40.67 and $38.56 for the three months ended June 30, 2012 and 2011, respectively, and $39.12 and $37.49 for the six months ended June 30, 2012 and 2011, respectively.