Depreciation and Interest Charges on Property, Plant and Equipment (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Property, Plant and Equipment [Line Items]
Depreciation and amortization on PP&E	$ 15.0	$ 13.7	$ 30.8	$ 26.5
Interest charges capitalized (in construction in progress)	$ 0.1	$ 0.3	$ 0.2	$ 0.6