Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Reconciliation of Unrecognized Tax Benefits [Line Items]
Beginning balance	$ 5.7	[1]
Additions based on tax positions related to current year	1.4	[1]
Additions for tax positions of prior years	2.0	[1]
Reductions for tax positions of prior years	(0.1)	[1]
Settlements		[1]
Net, current activity	3.3	[1]
Ending balance	$ 9.0	[1]

[1] Unrecognized state tax liabilities are not adjusted for the federal tax impact.