Fair Value Disclosures - Financial Assets and Liabilities Accounted for at Fair Value on Recurring Basis (Footnote) (Detail) - USD ($)	May. 31, 2015	Nov. 30, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of equity options transferred from Level 1 to Level 2 within Financial instruments owned	$ 0	$ 6,100,000
Fair value of equity options transferred from Level 1 to Level 2 within Financial instruments sold, not yet purchased		6,600,000
Assets at fair value segregated for regulatory purposes	525,000,000	453,700,000
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Increase corporate debt obligations		33,200,000
Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value segregated for regulatory purposes	$ 190,000,000	$ 545,000,000