Fair Value Disclosures - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Aug. 31, 2018	Aug. 31, 2017	Aug. 31, 2018	Aug. 31, 2017	Nov. 30, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3	$ 13,600	$ 63,500	$ 49,100	$ 26,500
Transfers of assets from Level 3 to Level 2	13,800	35,700	10,000	49,500
Net gains/(losses) on Level 3 assets (realized and unrealized)	9,800	6,000	10,400	(900)
Net gains/(losses) on Level 3 liabilities (realized and unrealized)	(4,400)	6,000	26,800	1,500
Aggregate fair value of loans and other receivables on nonaccrual status and/or 90 days or greater past due	77,000		77,000		$ 55,100
Loans and other receivables greater than 90 days past due	25,600		25,600		37,400
Cash and securities segregated and on deposit for regulatory purposes with clearing and depository organizations	913,456		913,456		578,014
Level 1
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Cash and securities segregated and on deposit for regulatory purposes with clearing and depository organizations	34,800		34,800		$ 99,700
Corporate equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 3 to Level 2	2,600		2,500
Transfers of liabilities from Level 2 to Level 3	0	0	0	0
Net gains/(losses) on Level 3 assets (realized and unrealized)	12,128	4,344	30,098	3,416
Net gains/(losses) on Level 3 liabilities (realized and unrealized)	326	107	365	134
Corporate debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3				8,100
Transfers of liabilities from Level 2 to Level 3	0	0	0	0
Net gains/(losses) on Level 3 assets (realized and unrealized)	1,057	(2,350)	1,090	(3,280)
Net gains/(losses) on Level 3 liabilities (realized and unrealized)	39	0	39	(1)
CDOs and CLOs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3			8,700	9,600
Transfers of assets from Level 3 to Level 2	3,700
Net gains/(losses) on Level 3 assets (realized and unrealized)	567	(6,119)	(2,323)	(13,902)
Municipal securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net gains/(losses) on Level 3 assets (realized and unrealized)				(1,547)
RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3	2,900
Transfers of assets from Level 3 to Level 2		14,600	4,600
Net gains/(losses) on Level 3 assets (realized and unrealized)	(66)	(263)	(7,334)	(1,446)
Investments at fair value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net gains/(losses) on Level 3 assets (realized and unrealized)	0	1,703	417	4,698
Other ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3	3,900	46,400
Transfers of assets from Level 3 to Level 2		13,500
Net gains/(losses) on Level 3 assets (realized and unrealized)	(2,269)	(6,454)	(7,528)	(15,338)
CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3	2,600		17,000
Transfers of assets from Level 3 to Level 2	4,600
Transfers of liabilities from Level 2 to Level 3	0	0	0	0
Net gains/(losses) on Level 3 assets (realized and unrealized)	(222)	(125)	(1,236)	(1,180)
Net gains/(losses) on Level 3 liabilities (realized and unrealized)	70	(35)	(35)	35
Loans and other receivables
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3			15,300
Transfers of assets from Level 3 to Level 2				28,300
Net gains/(losses) on Level 3 assets (realized and unrealized)	(1,353)	15,261	(2,812)	27,709
Long-term debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers of liabilities from Level 2 to Level 3	0		107,424
Net gains/(losses) on Level 3 liabilities (realized and unrealized)	3,004		(25,078)
Other changes in fair value	$ (6,842)	$ (1,854)	$ 33,626	$ 2,786