Share Repurchase Activity (Parenthetical) (Detail) (USD $) In Millions, except Share data	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Stockholders Equity Note [Line Items]
Number of shares repurchased	1,543,069	[1]	48,904	[1]	3,886,521	[1]	3,188,945	[1]
Share repurchase program, amount remaining for share repurchases					$ 363.0
Share repurchase program, approved amount					$ 500.0
Share Repurchase Program, 2011
Stockholders Equity Note [Line Items]
Number of shares repurchased					500,000

[1] The nine months ended September 30, 2011 includes 500,000 shares the Company repurchased directly from ValueAct Capital Master Fund L.P. in a private transaction.