Depreciation and Interest Charges on Property, Plant and Equipment (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Property, Plant and Equipment [Line Items]
Depreciation and amortization on PP&E	$ 14.1	$ 13.7	$ 44.9	$ 40.2
Interest charges capitalized (in construction in progress)	$ 0.1	$ 0.4	$ 0.3	$ 1.0