Share Repurchase Activity (Parenthetical) (Detail) (USD $) In Millions, except Share data	3 Months Ended				6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010
Stockholders Equity Note [Line Items]
Number of shares repurchased	932,624	[1]	1,636,341	[1]	2,343,452	[1]	3,140,041	[1]
Share repurchase program, amount remaining for share repurchases					$ 416.2
Share repurchase program, approved amount					$ 500.0
Share Repurchase Program, 2011
Stockholders Equity Note [Line Items]
Number of shares repurchased					500,000

[1] The 2010 share repurchases were made under the Company's previously authorized share repurchase program. The share repurchases for the six months ended June 30, 2011 includes 500,000 shares the Company repurchased directly from ValueAct Capital Master Fund L.P. ("ValueAct Capital") in February 2011 under a stock purchase agreement between the Company and ValueAct Capital.