Summary Of Changes In Stock Options Outstanding (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	6 Months Ended		12 Months Ended
	Jun. 30, 2012		Dec. 31, 2012
Options
Beginning Balance	1.2		1.2
Exercised	(0.7)	[1]
Ending Balance	0.5
Per Share Weighted Average Exercise Price
Beginning Balance	$ 10.93		$ 10.93
Exercised	$ 10.87	[1]
Ending Balance	$ 10.99
Weighted Average Remaining Contractual Term
Vested and outstanding	1 year 5 months 23 days		1 year 5 months 19 days
Aggregate Intrinsic Value
Beginning Balance	$ 27.7
Ending Balance	$ 17.1

[1] Options exercised during the six months ended June 30, 2012 had an intrinsic value of $18.7 million.