Fair Value Disclosures - Quantitative Information about Significant Unobservable Inputs Used in Level 3 Fair Value Measurements (Detail) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Aug. 31, 2017 USD ($) $ / shares	Nov. 30, 2016 USD ($) T / d $ / shares	May 31, 2017 USD ($)	Aug. 31, 2016 USD ($)	May 31, 2016 USD ($)	Nov. 30, 2015 USD ($)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Value of asset excluded from significant unobservable inputs | $	$ 23,700	$ 131,500
Value of liability excluded from significant unobservable inputs | $	4,000	1,600
Corporate equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value | $	22,174	21,739	$ 20,548	$ 22,195	$ 48,816	$ 40,906
Corporate debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value | $	25,015	25,005	24,727	35,007	24,113	25,876
CDOs and CLOs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value | $	38,203	54,354	27,255	44,070	52,710	85,092
RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value | $	20,649	38,772	33,032	46,881	63,308	70,263
CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value | $	17,636	20,580	16,263	24,593	24,983	14,326
Other ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value | $	68,946	40,911	43,349	61,112	43,033	42,925
Loans and other receivables
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value | $	62,656	81,872	49,365	78,457	104,399	189,289
Investments at fair value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value | $	90,417	96,369	$ 89,006	$ 85,036	$ 57,765	$ 53,120
Financial instruments owned | Derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value | $	2,671	6,429
Financial instruments owned | Corporate equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value | $	17,964	19,799
Financial instruments owned | Corporate debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value | $	25,015	25,005
Financial instruments owned | CDOs and CLOs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value | $	38,203	33,016
Financial instruments owned | RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value | $	20,649	38,772
Financial instruments owned | CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value | $	17,636	20,580
Financial instruments owned | Other ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value | $	68,946	40,911
Financial instruments owned | Loans and other receivables
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Instruments owned, fair value | $	59,398	54,347
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 | $	74,190	42,907
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 | $	$ 7,753	$ 9,870
Level 3 | Financial instruments owned | Derivatives | Equity swaps | Comparable pricing
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Comparable asset price		$ 102
Level 3 | Financial instruments owned | Derivatives | Credit default swaps | Market approach
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Constant default rate / Credit spread		2.65%
Level 3 | Financial instruments owned | Derivatives | Interest rate swaps | Market approach
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), 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]
Significant Unobservable Input(s), Underlying stock price (in dollars per share)	$ 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]
Significant Unobservable Input(s), Price	3
Significant Unobservable Input(s), Underlying stock price (in dollars per share)		$ 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]
Significant Unobservable Input(s), Price	75
Significant Unobservable Input(s), Underlying stock price (in dollars per share)		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]
Significant Unobservable Input(s), Price	59
Significant Unobservable Input(s), Underlying stock price (in dollars per share)		15
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]
Significant Unobservable Input(s), Underlying stock price (in dollars per share)		218
Significant Unobservable Input(s), Comparable asset price	9	$ 11
Level 3 | Financial instruments owned | Corporate equity securities | Non-exchange-traded securities | Present value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Average silver production (tons per day) | T / d		666
Level 3 | Financial instruments owned | Corporate debt securities | Market approach
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Price	$ 15
Significant Unobservable Input(s), Estimated recovery percentage	17.00%
Significant Unobservable Input(s), Transaction level (in dollars per share)		$ 30
Level 3 | Financial instruments owned | Corporate debt securities | Convertible bond model
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Volatility	40.00%	40.00%
Significant Unobservable Input(s), Discount rate/yield	8.00%	9.00%
Level 3 | Financial instruments owned | CDOs and CLOs | Discounted cash flows
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Constant prepayment rate	20.00%
Significant Unobservable Input(s), Constant default rate / Credit spread	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]
Significant Unobservable Input(s), Discount rate/yield	9.00%
Significant Unobservable Input(s), Constant prepayment rate		10.00%
Significant Unobservable Input(s), Constant default rate / Credit spread		2.00%
Significant Unobservable Input(s), Loss severity	25.00%	25.00%
Significant Unobservable Input(s), Yield		7.00%
Level 3 | Financial instruments owned | CDOs and CLOs | Discounted cash flows | Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Discount rate/yield	23.00%
Significant Unobservable Input(s), Constant prepayment rate		20.00%
Significant Unobservable Input(s), Constant default rate / Credit spread		4.00%
Significant Unobservable Input(s), Loss severity	30.00%	70.00%
Significant Unobservable Input(s), Yield		17.00%
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]
Significant Unobservable Input(s), Discount rate/yield	12.00%
Significant Unobservable Input(s), Constant prepayment rate		19.00%
Significant Unobservable Input(s), Constant default rate / Credit spread		2.00%
Significant Unobservable Input(s), Loss severity	27.00%	40.00%
Significant Unobservable Input(s), Yield		12.00%
Level 3 | Financial instruments owned | CDOs and CLOs | Scenario analysis | Minimum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Estimated recovery percentage	6.00%	28.00%
Level 3 | Financial instruments owned | CDOs and CLOs | Scenario analysis | Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Estimated recovery percentage	40.00%	38.00%
Level 3 | Financial instruments owned | CDOs and CLOs | Scenario analysis | Weighted Average
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Estimated recovery percentage	24.00%	31.00%
Level 3 | Financial instruments owned | RMBS | Discounted cash flows | Minimum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Discount rate/yield	8.00%
Significant Unobservable Input(s), Cumulative loss rate	5.00%
Significant Unobservable Input(s), Duration (years)	3 years
Significant Unobservable Input(s), Constant prepayment rate		0.00%
Significant Unobservable Input(s), Constant default rate / Credit spread		1.00%
Significant Unobservable Input(s), Loss severity		35.00%
Significant Unobservable Input(s), Yield		2.00%
Level 3 | Financial instruments owned | RMBS | Discounted cash flows | Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Discount rate/yield	10.00%
Significant Unobservable Input(s), Cumulative loss rate	30.00%
Significant Unobservable Input(s), Duration (years)	10 years
Significant Unobservable Input(s), Constant prepayment rate		11.00%
Significant Unobservable Input(s), Constant default rate / Credit spread		7.00%
Significant Unobservable Input(s), Loss severity		100.00%
Significant Unobservable Input(s), Yield		10.00%
Level 3 | Financial instruments owned | RMBS | Discounted cash flows | Weighted Average
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Discount rate/yield	9.00%
Significant Unobservable Input(s), Cumulative loss rate	13.00%
Significant Unobservable Input(s), Duration (years)	5 years
Significant Unobservable Input(s), Constant prepayment rate		5.00%
Significant Unobservable Input(s), Constant default rate / Credit spread		3.00%
Significant Unobservable Input(s), Loss severity		62.00%
Significant Unobservable Input(s), Yield		6.00%
Level 3 | Financial instruments owned | CMBS | Discounted cash flows | Minimum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Discount rate/yield	2.00%
Significant Unobservable Input(s), Cumulative loss rate	0.00%	5.00%
Significant Unobservable Input(s), Duration (years)	1 year
Significant Unobservable Input(s), Yield		6.00%
Level 3 | Financial instruments owned | CMBS | Discounted cash flows | Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Discount rate/yield	21.00%
Significant Unobservable Input(s), Cumulative loss rate	58.00%	95.00%
Significant Unobservable Input(s), Duration (years)	3 years
Significant Unobservable Input(s), Yield		11.00%
Level 3 | Financial instruments owned | CMBS | Discounted cash flows | Weighted Average
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Discount rate/yield	11.00%
Significant Unobservable Input(s), Cumulative loss rate	29.00%	39.00%
Significant Unobservable Input(s), Duration (years)	2 years
Significant Unobservable Input(s), Yield		8.00%
Level 3 | Financial instruments owned | Other ABS | Market approach
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Price	$ 100	$ 72
Level 3 | Financial instruments owned | Other ABS | Discounted cash flows | Minimum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Discount rate/yield	4.00%
Significant Unobservable Input(s), Cumulative loss rate	0.00%
Significant Unobservable Input(s), Duration (years)	1 year
Significant Unobservable Input(s), Constant prepayment rate		4.00%
Significant Unobservable Input(s), Constant default rate / Credit spread		0.00%
Significant Unobservable Input(s), Loss severity		0.00%
Significant Unobservable Input(s), Yield		4.00%
Level 3 | Financial instruments owned | Other ABS | Discounted cash flows | Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Discount rate/yield	12.00%
Significant Unobservable Input(s), Cumulative loss rate	25.00%
Significant Unobservable Input(s), Duration (years)	10 years
Significant Unobservable Input(s), Constant prepayment rate		20.00%
Significant Unobservable Input(s), Constant default rate / Credit spread		31.00%
Significant Unobservable Input(s), Loss severity		100.00%
Significant Unobservable Input(s), Yield		17.00%
Level 3 | Financial instruments owned | Other ABS | Discounted cash flows | Weighted Average
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Discount rate/yield	8.00%
Significant Unobservable Input(s), Cumulative loss rate	20.00%
Significant Unobservable Input(s), Duration (years)	2 years
Significant Unobservable Input(s), Constant prepayment rate		14.00%
Significant Unobservable Input(s), Constant default rate / Credit spread		13.00%
Significant Unobservable Input(s), Loss severity		90.00%
Significant Unobservable Input(s), Yield		15.00%
Level 3 | Financial instruments owned | Other ABS | Scenario analysis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Estimated recovery percentage	23.00%
Level 3 | Financial instruments owned | Loans and other receivables | Market approach
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), EBITDA multiple	1.6	3.3
Significant Unobservable Input(s), Transaction level (in dollars per share)		$ 0.42
Level 3 | Financial instruments owned | Loans and other receivables | Market approach | Minimum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Price	$ 60
Significant Unobservable Input(s), Discount rate/yield		2.00%
Level 3 | Financial instruments owned | Loans and other receivables | Market approach | Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Price	100
Significant Unobservable Input(s), Discount rate/yield		4.00%
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]
Significant Unobservable Input(s), Price	$ 95
Significant Unobservable Input(s), Discount rate/yield		3.00%
Level 3 | Financial instruments owned | Loans and other receivables | Present value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Average silver production (tons per day) | T / d		666
Level 3 | Financial instruments owned | Loans and other receivables | Scenario analysis | Minimum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Estimated recovery percentage	10.00%	6.00%
Level 3 | Financial instruments owned | Loans and other receivables | Scenario analysis | Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Estimated recovery percentage	107.00%	50.00%
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]
Significant Unobservable Input(s), Estimated recovery percentage	67.00%	37.00%
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]
Significant Unobservable Input(s), Price		$ 25,815,720
Significant Unobservable Input(s), Transaction level (in dollars per share)	$ 3	250
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]
Significant Unobservable Input(s), Price	7
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]
Significant Unobservable Input(s), Price	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]
Significant Unobservable Input(s), Price	$ 123
Level 3 | Financial Instruments Sold, Not Yet Purchased | Derivatives | Equity swaps | Comparable pricing
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Comparable asset price		$ 102
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]
Significant Unobservable Input(s), Default probability	0.00%
Level 3 | Financial Instruments Sold, Not Yet Purchased | Derivatives | Equity options | Option model
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Volatility		45.00%
Level 3 | Financial Instruments Sold, Not Yet Purchased | Derivatives | Equity options | Default rate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Significant Unobservable Input(s), Default probability		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]
Significant Unobservable Input(s), Discount rate/yield		4.00%
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]
Significant Unobservable Input(s), Discount rate/yield	23.00%
Significant Unobservable Input(s), Constant prepayment rate	20.00%	20.00%
Significant Unobservable Input(s), Constant default rate / Credit spread	2.00%	2.00%
Significant Unobservable Input(s), Loss severity	25.00%	25.00%
Significant Unobservable Input(s), Yield		16.00%