Fair Value Disclosures - Quantitative Information about Significant Unobservable Inputs Used in Level 3 Fair Value Measurements (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Feb. 28, 2018	Nov. 30, 2017	Feb. 28, 2017	Nov. 30, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Value of asset excluded from significant unobservable inputs	$ 13,100	$ 21,100
Value of liability excluded from significant unobservable inputs	10,900	4,200
Corporate equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value	35,412	22,009	$ 20,580	$ 21,739
Corporate debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value	26,103	26,036	33,467	25,005
CDOs and CLOs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value	26,433	30,004	45,354	54,354
RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value	21,762	26,077	39,259	38,772
CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value	15,103	12,419	20,653	20,580
Other ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value	51,288	61,129	37,702	40,911
Loans and other receivables
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value	62,043	47,304	53,172	81,872
Investments at fair value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value	79,879	93,454	$ 83,785	$ 96,369
Financial instruments owned | Derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value	4,712	9,295
Financial instruments owned | Corporate equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value	30,335	18,109
Financial instruments owned | Corporate debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value	26,103	26,036
Financial instruments owned | CDOs and CLOs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value	26,433	30,004
Financial instruments owned | RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value	21,762	26,077
Financial instruments owned | CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value	15,103	12,419
Financial instruments owned | Other ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value	51,288	61,129
Financial instruments owned | Loans and other receivables
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value	54,004	46,121
Financial instruments owned | Investments at fair value | Private equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value	79,879	77,423
Financial Instruments Sold, Not Yet Purchased | Derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments sold, not yet purchased, fair value	$ 11,594	$ 16,041
Level 3 | Financial instruments owned | Derivatives | Total return swaps | Market approach
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price	$ 102
Level 3 | Financial instruments owned | Derivatives | Total return swaps | Market approach | Minimum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price		$ 101
Level 3 | Financial instruments owned | Derivatives | Total return swaps | Market approach | Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price		106
Level 3 | Financial instruments owned | Derivatives | Total return swaps | Market approach | Weighted Average
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price		$ 103
Level 3 | Financial instruments owned | Derivatives | Interest rate swaps | Market approach
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Constant default rate / Credit spread		8.00%
Level 3 | Financial instruments owned | Corporate equity securities | Non-exchange-traded securities | Market approach
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Underlying stock price	11	$ 6
Level 3 | Financial instruments owned | Corporate equity securities | Non-exchange-traded securities | Market approach | Minimum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price	3	3
Level 3 | Financial instruments owned | Corporate equity securities | Non-exchange-traded securities | Market approach | Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price	750	75
Level 3 | Financial instruments owned | Corporate equity securities | Non-exchange-traded securities | Market approach | Weighted Average
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price	183	33
Level 3 | Financial instruments owned | Corporate equity securities | Non-exchange-traded securities | Comparable pricing
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Comparable asset price	10	7
Level 3 | Financial instruments owned | Corporate debt securities | Market approach
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price	$ 10	$ 10
Estimated recovery percentage		17.00%
Level 3 | Financial instruments owned | Corporate debt securities | Market approach | Minimum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Estimated recovery percentage	2.00%
Level 3 | Financial instruments owned | Corporate debt securities | Market approach | Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Estimated recovery percentage	32.00%
Level 3 | Financial instruments owned | Corporate debt securities | Market approach | Weighted Average
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Estimated recovery percentage	25.00%
Level 3 | Financial instruments owned | Corporate debt securities | Comparable pricing
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Comparable asset price	$ 47
Level 3 | Financial instruments owned | Corporate debt securities | Convertible bond model
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Discount rate/yield	9.00%	8.00%
Volatility	40.00%	40.00%
Level 3 | Financial instruments owned | CDOs and CLOs | Discounted cash flows
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Constant prepayment rate	20.00%	20.00%
Constant default rate / Credit spread	2.00%	2.00%
Level 3 | Financial instruments owned | CDOs and CLOs | Discounted cash flows | Minimum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Discount rate/yield	6.00%	3.00%
Loss severity	25.00%	25.00%
Level 3 | Financial instruments owned | CDOs and CLOs | Discounted cash flows | Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Discount rate/yield	31.00%	26.00%
Loss severity	30.00%	30.00%
Level 3 | Financial instruments owned | CDOs and CLOs | Discounted cash flows | Weighted Average
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Discount rate/yield	17.00%	12.00%
Loss severity	26.00%	26.00%
Level 3 | Financial instruments owned | CDOs and CLOs | Scenario analysis | Minimum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Estimated recovery percentage	7.00%	8.00%
Level 3 | Financial instruments owned | CDOs and CLOs | Scenario analysis | Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Estimated recovery percentage	40.00%	40.00%
Level 3 | Financial instruments owned | CDOs and CLOs | Scenario analysis | Weighted Average
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Estimated recovery percentage	23.00%	22.00%
Level 3 | Financial instruments owned | RMBS | Discounted cash flows | Minimum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Discount rate/yield	3.00%	6.00%
Cumulative loss rate	3.00%	3.00%
Duration (years)	2 years	2 years
Level 3 | Financial instruments owned | RMBS | Discounted cash flows | Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Discount rate/yield	9.00%	10.00%
Cumulative loss rate	19.00%	19.00%
Duration (years)	4 years	4 years
Level 3 | Financial instruments owned | RMBS | Discounted cash flows | Weighted Average
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Discount rate/yield	7.00%	8.00%
Cumulative loss rate	9.00%	10.00%
Duration (years)	3 years	3 years
Level 3 | Financial instruments owned | CMBS | Discounted cash flows | Minimum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Discount rate/yield	3.00%	2.00%
Cumulative loss rate	7.00%	8.00%
Duration (years)	0 years	1 year
Level 3 | Financial instruments owned | CMBS | Discounted cash flows | Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Discount rate/yield	24.00%	26.00%
Cumulative loss rate	65.00%	65.00%
Duration (years)	2 years	3 years
Level 3 | Financial instruments owned | CMBS | Discounted cash flows | Weighted Average
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Discount rate/yield	17.00%	12.00%
Cumulative loss rate	33.00%	44.00%
Duration (years)	1 year	2 years
Level 3 | Financial instruments owned | CMBS | Scenario analysis | Minimum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price	$ 49	$ 52
Estimated recovery percentage	26.00%	26.00%
Level 3 | Financial instruments owned | CMBS | Scenario analysis | Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price	$ 52	$ 56
Estimated recovery percentage	32.00%	32.00%
Level 3 | Financial instruments owned | CMBS | Scenario analysis | Weighted Average
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price	$ 50	$ 54
Estimated recovery percentage	28.00%	28.00%
Level 3 | Financial instruments owned | Other ABS | Market approach
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price		$ 100
Level 3 | Financial instruments owned | Other ABS | Discounted cash flows | Minimum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Discount rate/yield	5.00%	5.00%
Cumulative loss rate	0.00%	0.00%
Duration (years)	1 year	1 year
Level 3 | Financial instruments owned | Other ABS | Discounted cash flows | Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Discount rate/yield	11.00%	39.00%
Cumulative loss rate	27.00%	33.00%
Duration (years)	6 years	6 years
Level 3 | Financial instruments owned | Other ABS | Discounted cash flows | Weighted Average
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Discount rate/yield	8.00%	9.00%
Cumulative loss rate	22.00%	23.00%
Duration (years)	2 years	2 years
Level 3 | Financial instruments owned | Other ABS | Scenario analysis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Estimated recovery percentage	11.00%	14.00%
Level 3 | Financial instruments owned | Loans and other receivables | Market approach
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price	$ 97
Estimated recovery percentage		76.00%
Transaction level	$ 100
Level 3 | Financial instruments owned | Loans and other receivables | Market approach | Minimum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price		$ 54
Estimated recovery percentage	23.00%
Level 3 | Financial instruments owned | Loans and other receivables | Market approach | Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price		100
Estimated recovery percentage	79.00%
Level 3 | Financial instruments owned | Loans and other receivables | Market approach | Weighted Average
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price		$ 95
Estimated recovery percentage	36.00%
Level 3 | Financial instruments owned | Loans and other receivables | Scenario analysis | Minimum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Estimated recovery percentage	62.00%	13.00%
Level 3 | Financial instruments owned | Loans and other receivables | Scenario analysis | Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Estimated recovery percentage	107.00%	107.00%
Level 3 | Financial instruments owned | Loans and other receivables | Scenario analysis | Weighted Average
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Estimated recovery percentage	90.00%	78.00%
Level 3 | Financial instruments owned | Investments at fair value | Private equity securities | Market approach
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price		$ 7
Level 3 | Financial instruments owned | Investments at fair value | Private equity securities | Market approach | Minimum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price	$ 0
Transaction level		3
Level 3 | Financial instruments owned | Investments at fair value | Private equity securities | Market approach | Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price	250
Transaction level		250
Level 3 | Financial instruments owned | Investments at fair value | Private equity securities | Market approach | Weighted Average
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price	104
Transaction level		172
Level 3 | Financial Instruments Sold, Not Yet Purchased | Derivatives | Total return swaps | Market approach
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price	$ 102
Level 3 | Financial Instruments Sold, Not Yet Purchased | Derivatives | Total return swaps | Market approach | Minimum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price		101
Level 3 | Financial Instruments Sold, Not Yet Purchased | Derivatives | Total return swaps | Market approach | Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price		106
Level 3 | Financial Instruments Sold, Not Yet Purchased | Derivatives | Total return swaps | Market approach | Weighted Average
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price		$ 103
Level 3 | Financial Instruments Sold, Not Yet Purchased | Derivatives | Equity options | Option model/default rate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Default probability	0.00%	0.00%
Level 3 | Financial Instruments Sold, Not Yet Purchased | Derivatives | Unfunded commitments | Market approach
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price	$ 97	$ 99
Level 3 | Financial Instruments Sold, Not Yet Purchased | Derivatives | Variable funding note swaps | Discounted cash flows
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Discount rate/yield	31.00%	26.00%
Constant prepayment rate	20.00%	20.00%
Constant default rate / Credit spread	2.00%	2.00%
Loss severity	25.00%	25.00%