Fair Value of Assets (Liabilities) Not Measured at Fair Value In Consolidated Balance Sheets (Parenthetical) (Detail) (Fixed Rate, USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fixed Rate
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long term debt, carrying value	$ 125.0	$ 125.0