Interest Cost Capitalized and Depreciation and Amortization Expense for Property and Equipment (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Interest Expense [Line Items]
Interest cost capitalized	$ 1.6	$ 1.2	$ 3.9	$ 2.9
Depreciation and amortization expense for property and equipment	$ 42.8	$ 34.2	$ 131.1	$ 102.1