Stock-Based Compensation (Detail) - Summary Of Changes In Stock Options Outstanding (USD $) In Millions, except Per Share data, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2012		Dec. 31, 2011
Options outstanding	0.4		1.2
Per Share Weighted- Average Exercise Price (in Dollars per share)	$ 11.13		$ 10.93
Weighted Average Remaining Contractual Term	1 year 109 days		1 year 171 days
Aggregate Intrinsic Value (in Dollars)	$ 15.6		$ 27.7
Exercised (1)	(0.8)	[1]
Exercised (1) (in Dollars per share)	$ 10.80	[1]
Exercised (1) (in Dollars)		[1]

[1] Options exercised during the nine months ended September 30, 2012 had an intrinsic value of $22.1 million.