Fair Value Disclosures - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Feb. 28, 2017	Feb. 29, 2016	Nov. 30, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investments at fair value	$ 24,200		$ 24,300
Transfers of assets from Level 2 to Level 3	49,900	$ 119,000
Transfers of assets from Level 3 to Level 2	39,800	100,800
Net gains/(losses) on Level 3 assets (realized and unrealized)	(10,200)	(42,200)
Net gains/(losses) on Level 3 liabilities (realized and unrealized)	4,200	(10,000)
Aggregate fair value of loans and other receivables on nonaccrual status and/or greater than 90 days past due	253,800		29,800
Loans and other receivables greater than 90 days past due	25,800		18,900
Cash and securities segregated and on deposit for regulatory purposes or deposited with clearing and depository organizations	705,313		857,337
Long-term debt [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Other changes in fair value	3,417	6,858
CDOs and CLOs [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3	18,100	39,500
Transfers of assets from Level 3 to Level 2		21,000
Net gains/(losses) on Level 3 assets (realized and unrealized)	(7,594)	(16,573)
Municipal securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net gains/(losses) on Level 3 assets (realized and unrealized)	(636)
RMBS [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3	13,700	20,400
Transfers of assets from Level 3 to Level 2		15,900
Net gains/(losses) on Level 3 assets (realized and unrealized)	(253)	(4,548)
Investments at fair value [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3		26,100
Net gains/(losses) on Level 3 assets (realized and unrealized)	(2,199)	(16,515)
Other ABS [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 3 to Level 2		28,800
Net gains/(losses) on Level 3 assets (realized and unrealized)	(1,788)	1,662
Corporate equity securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 3 to Level 2		19,200
Net gains/(losses) on Level 3 assets (realized and unrealized)	532	3,071
CMBS [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net gains/(losses) on Level 3 assets (realized and unrealized)	(1,420)	(971)
Loans and other receivables [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 3 to Level 2	28,200
Net gains/(losses) on Level 3 assets (realized and unrealized)	4,950	(5,772)
Corporate debt securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Transfers of assets from Level 2 to Level 3	11,600
Net gains/(losses) on Level 3 assets (realized and unrealized)	$ (1,793)	$ (2,602)
3.875% Convertible Senior Debentures due 2029 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt instrument interest rate	3.875%
Level 1 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Cash and securities segregated and on deposit for regulatory purposes or deposited with clearing and depository organizations	$ 99,900		$ 99,900