Location and Amounts of Gains and Losses on Derivative Instrument Designated as Fair Value Hedge (Detail) (Interest rate swap contract, Interest Expense, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Interest rate swap contract | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Gain Recognized on Swap	$ 1.2	$ 11.4	$ 0.7
Loss Recognized on Long-Term Debt	$ (1.2)	$ (11.4)	$ (0.7)