Summary Of Changes In Stock Options Outstanding (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012 Year
Options
Beginning Balance	1.2
Expired
Exercised	(0.4)	[1]
Ending Balance	0.8
Per Share Weighted Average Exercise Price
Beginning Balance	$ 10.93
Expired
Exercised	$ 11.03	[1]
Ending Balance	$ 10.87
Weighted Average Remaining Contractual Term
Beginning Balance	1.47
Ending Balance	1.35
Aggregate Intrinsic Value
Beginning Balance	$ 27.7
Ending Balance	$ 24.1

[1] Options exercised during the three months ended March 31, 2012 had an intrinsic value of $11.5 million.