Summary of Total Indebtedness (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Fair value of interest rate swap	$ 11.9	$ 20.5
Series Two Thousand Five Dash One Notes [Member]
Debt Instrument [Line Items]
Fair value of interest rate swap	5.8	10.3
Twenty Ten Senior Notes [Member]
Debt Instrument [Line Items]
Unamortized discount	2.2	2.2
Twenty Twelve Senior Notes [Member]
Debt Instrument [Line Items]
Unamortized discount	3.4	3.5
Twenty Thirteen Senior Notes [Member]
Debt Instrument [Line Items]
Unamortized discount	$ 2.7	$ 2.8