Investments (Schedule Of Aging Of Unrealized Losses On Investments) (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Less Than One Year [Member]
Schedule of Investments [Line Items]
Unrealized losses less than one year	$ 0.1	$ 0.1
One Year Or Greater [Member]
Schedule of Investments [Line Items]
Unrealized losses less than one year	$ 0.1	$ 0.1