Fair Value Disclosures - Financial Assets and Liabilities Accounted for at Fair Value on Recurring Basis (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Nov. 30, 2012 Predecessor [Member]	May 31, 2013 Successor [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. government securities at fair value segregated for regulatory purposes	$ 404.3	$ 284.3