Summary of Total Indebtedness (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Fair value of interest rate swap	$ 20.5	$ 15.2
Series 2005-1 Notes
Debt Instrument [Line Items]
Fair value of interest rate swap	10.3	13.8
2010 Senior Notes
Debt Instrument [Line Items]
Unamortized discount	2.2	2.6
2012 Senior Notes
Debt Instrument [Line Items]
Unamortized discount	3.5	3.8
2013 Senior Notes
Debt Instrument [Line Items]
Unamortized discount	$ 2.8