Fair Value Disclosures (Financial Instruments Not Measured at Fair Value, Narrative) (Details) - USD ($) $ in Thousands	Aug. 31, 2020	Nov. 30, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and securities segregated under federal and other regulations	$ 986,117	$ 796,797
US treasury securities \| Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and securities segregated under federal and other regulations	$ 55,900	$ 35,000

Amount of cash subject to withdrawal restrictions, restricted deposits held as compensating balances, and cash and securities segregated in compliance with regulations (such as cash deposited in a special reserve account for the exclusive benefit of customers).

No definition available.

Name:	us-gaap_CashAndSecuritiesSegregatedUnderFederalAndOtherRegulations
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant