Related Party Transactions - Jefferies (Detail) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Dec. 31, 2018	May 31, 2019	May 31, 2018	May 31, 2019	May 31, 2018	Jan. 29, 2019	Nov. 30, 2018
Related Party Transaction [Line Items]
Payables-brokers, dealers and clearing organizations		$ 2,465,693,000		$ 2,465,693,000			$ 2,448,059,000
Financial instruments owned, at fair value		16,095,884,000		16,095,884,000			16,399,526,000
Financial instruments sold, not yet purchased, at fair value		10,113,390,000		10,113,390,000			9,478,944,000
Jefferies | Affiliated Entity
Related Party Transaction [Line Items]
Charges to Jefferies for services provided		9,600,000	$ 14,100,000	26,100,000	$ 30,300,000
Charges from Jefferies for services received		600,000	2,300,000	1,300,000	4,700,000
Receivable from Jefferies		600,000		600,000			1,200,000
Payable to Jefferies		3,700,000		3,700,000			2,900,000
Payments of distributions to affiliates				53,700,000
Distribution to affiliates, approved amount						$ 100,000,000.0
Distribution payable accrued during period				55,000,000.0
Proceeds from sale of securities		17,900,000		17,900,000
Payments to acquire securities				885,600,000
Net gain (loss) on investments				0
Jefferies | Affiliated Entity | Accrued expenses and other liabilities
Related Party Transaction [Line Items]
Net current tax payable		28,400,000		28,400,000			34,100,000
Payment made to related party related to tax sharing agreement	$ 35,000,000.0
Jefferies | Affiliated Entity | Payables - brokers, dealers and clearing organizations
Related Party Transaction [Line Items]
Payables-brokers, dealers and clearing organizations		14,200,000		14,200,000			9,900,000
Jefferies | Affiliated Entity | Investment banking
Related Party Transaction [Line Items]
Charges to Jefferies for services provided		7,900,000	0	7,900,000	0
Jefferies | Affiliated Entity | Commissions and other fees
Related Party Transaction [Line Items]
Charges to Jefferies for services provided		100,000	400,000	300,000	400,000
Jefferies | Affiliated Entity | Principal transactions
Related Party Transaction [Line Items]
Charges to Jefferies for services provided		0	0	0	100,000
Jefferies | Affiliated Entity | Other revenues
Related Party Transaction [Line Items]
Charges to Jefferies for services provided		400,000	200,000	900,000	400,000
Hedge Fund Managed By Jefferies | Affiliated Entity
Related Party Transaction [Line Items]
Net gain (loss) on investments		1,300,000	$ 800,000	2,300,000	$ 4,500,000
Investment in related party		220,900,000		220,900,000			218,700,000
Corporate debt securities
Related Party Transaction [Line Items]
Financial instruments sold, not yet purchased, at fair value		1,920,135,000		1,920,135,000			1,506,140,000
Corporate debt securities | Jefferies | Affiliated Entity
Related Party Transaction [Line Items]
Financial instruments owned, at fair value		100,000		100,000			300,000
Financial instruments sold, not yet purchased, at fair value		200,000		200,000
Director | Affiliated Entity
Related Party Transaction [Line Items]
Investment in related party		3,600,000		3,600,000			4,600,000
Director | Hedge Fund Managed By Jefferies | Affiliated Entity
Related Party Transaction [Line Items]
Investment in related party		$ 2,500,000		$ 2,500,000			$ 2,700,000