Fair Value Disclosures - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	May. 31, 2015	May. 31, 2014	May. 31, 2015	May. 31, 2014	Nov. 30, 2014
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments at fair value	$ 42,500,000		$ 42,500,000		$ 42,200,000
Other secured financings	709,567,000		709,567,000		605,824,000
Transfers of assets from Level 2 to Level 3	98,400,000	$ 95,200,000	155,000,000	$ 94,900,000
Transfers of assets from Level 3 to Level 2	96,400,000	59,400,000	87,000,000	55,300,000
Transfers of liabilities from Level 2 to Level 3		11,700,000		2,800,000
Transfers of liabilities from Level 3 to Level 2		3,900,000	3,000,000
Net gains/(losses) on Level 3 assets (realized and unrealized)	2,400,000	22,500,000	(17,300,000)	39,400,000
Net gains/(losses) on Level 3 liabilities (realized and unrealized)	5,000,000	(4,800,000)	(1,900,000)	(6,500,000)
Unadjusted net asset value of the funds			178,700,000		137,800,000
Unadjusted net liability value of the funds			500,000		300,000
Aggregate fair value of loans and other receivables	13,900,000		13,900,000		0
Loan and other receivables on nonaccrual status	332,000,000		332,000,000		274,600,000
Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Other secured financings	3,900,000		3,900,000		$ 7,800,000
Corporate debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Transfers of assets from Level 2 to Level 3	8,200,000	600,000	10,400,000	300,000
Transfers of liabilities from Level 2 to Level 3				100,000
Net gains/(losses) on Level 3 assets (realized and unrealized)	(532,000)	5,659,000	(796,000)	5,116,000
Derivative liabilities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Transfers of liabilities from Level 3 to Level 2				3,300,000
Corporate equity securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Transfers of assets from Level 2 to Level 3	1,400,000	11,600,000	1,600,000	11,500,000
Transfers of assets from Level 3 to Level 2	7,000,000	7,400,000	10,300,000	3,600,000
Net gains/(losses) on Level 3 assets (realized and unrealized)	8,030,000	(178,000)	7,066,000	(1,583,000)
Collateralized debt obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Transfers of assets from Level 2 to Level 3	48,000,000	7,100,000	27,300,000	14,300,000
Transfers of assets from Level 3 to Level 2	54,400,000	4,700,000	52,300,000	3,600,000
Net gains/(losses) on Level 3 assets (realized and unrealized)	(5,120,000)	4,706,000	(17,229,000)	14,169,000
Residential mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Transfers of assets from Level 2 to Level 3	30,000,000	5,500,000	20,300,000	20,900,000
Transfers of assets from Level 3 to Level 2	23,000,000	35,600,000	15,100,000	34,300,000
Net gains/(losses) on Level 3 assets (realized and unrealized)	(1,820,000)	(791,000)	(3,735,000)	(4,114,000)
Commercial mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Transfers of assets from Level 2 to Level 3	7,700,000	14,200,000	10,200,000	8,400,000
Transfers of assets from Level 3 to Level 2	5,500,000	2,300,000	3,500,000	400,000
Net gains/(losses) on Level 3 assets (realized and unrealized)	(789,000)	(903,000)	(1,124,000)	(2,191,000)
Other asset-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Transfers of assets from Level 2 to Level 3	2,100,000	29,900,000	2,100,000	25,500,000
Transfers of assets from Level 3 to Level 2	5,400,000	1,800,000		3,500,000
Net gains/(losses) on Level 3 assets (realized and unrealized)	(19,000)	(314,000)	(258,000)	(537,000)
Loans and other receivables [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Transfers of assets from Level 2 to Level 3	1,000,000	26,300,000	13,900,000	14,200,000
Transfers of assets from Level 3 to Level 2		1,100,000	5,300,000	2,600,000
Net gains/(losses) on Level 3 assets (realized and unrealized)	(748,000)	11,933,000	(5,795,000)	3,946,000
Investments at fair value [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Transfers of assets from Level 2 to Level 3			69,200,000
Transfers of assets from Level 3 to Level 2		6,500,000		7,200,000
Net gains/(losses) on Level 3 assets (realized and unrealized)	$ 3,380,000	$ 2,349,000	$ 4,615,000	$ 24,601,000
3.875% Convertible Senior Debentures due 2029 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt instrument interest rate	3.875%		3.875%
3.875% Convertible Senior Debentures due 2029 [Member] | Leucadia [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt instrument interest rate	3.875%		3.875%
Debt instrument maturity year			Nov. 01, 2029
Volatility curve used in valuing embedded option			252 days
Embedded conversion option [Member] | Leucadia [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt instrument maturity year			Nov. 01, 2017