Investments in Marketable Securities - Fair Value of Financial Assets and Liabilities Measured on Recurring Basis (Parenthetical) (Detail) (U.S. Treasury Notes and Bonds Conventional [Member], USD $) In Millions, unless otherwise specified	Jan. 31, 2014
U.S. Treasury Notes and Bonds Conventional [Member]
Assets And Liabilities Carrying Value And Fair Value [Line Items]
Investments reclassified from level 1 to level 2	$ 9.1