Related Party Transactions - Jefferies (Details) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended
	Dec. 31, 2018	Aug. 31, 2019	Aug. 31, 2018	Aug. 31, 2019	Aug. 31, 2018	Jan. 29, 2019	Nov. 30, 2018
Related Party Transaction [Line Items]
Payables-brokers, dealers and clearing organizations		$ 2,253,033,000		$ 2,253,033,000			$ 2,448,059,000
Financial instruments owned, at fair value		16,370,912,000		16,370,912,000			16,399,526,000
Financial instruments sold, not yet purchased, at fair value		10,296,315,000		10,296,315,000			9,478,944,000
Jefferies | Affiliated Entity
Related Party Transaction [Line Items]
Charges to Jefferies for services provided		9,800,000	$ 15,800,000	36,100,000	$ 46,100,000
Charges from Jefferies for services received		6,400,000	2,200,000	7,800,000	6,900,000
Receivable from Jefferies		2,100,000		2,100,000			1,200,000
Payable to Jefferies		8,700,000		8,700,000			2,900,000
Payments of distributions to affiliates				108,700,000
Distribution to affiliates, approved amount						$ 100,000,000.0
Distribution payable accrued during period		32,500,000
Net current tax receivable		5,600,000		5,600,000
Net current tax payable							34,100,000
Payment made to related party related to tax sharing agreement	$ 35,000,000.0
Proceeds from sale of securities		22,900,000		40,800,000
Payments to acquire securities				885,600,000
Net gain (loss) on investments				0
Payables-brokers, dealers and clearing organizations		22,700,000		22,700,000			9,900,000
Financial instruments sold, not yet purchased, at fair value		200,000		200,000
Jefferies | Affiliated Entity | Investment banking
Related Party Transaction [Line Items]
Charges to Jefferies for services provided		2,400,000	5,600,000	10,300,000	5,600,000
Jefferies | Affiliated Entity | Commissions and other fees
Related Party Transaction [Line Items]
Charges to Jefferies for services provided		0	100,000	300,000	500,000
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		1,100,000	300,000	2,000,000.0	700,000
Hedge Fund Managed By Jefferies | Affiliated Entity
Related Party Transaction [Line Items]
Net gain (loss) on investments		1,000,000.0	$ 500,000	3,300,000	$ 5,000,000.0
Investment in related party		222,100,000		222,100,000			218,700,000
Corporate debt securities
Related Party Transaction [Line Items]
Financial instruments sold, not yet purchased, at fair value		1,804,868,000		1,804,868,000			1,506,140,000
Corporate debt securities | Jefferies | Affiliated Entity
Related Party Transaction [Line Items]
Financial instruments owned, at fair value		3,100,000		3,100,000			300,000
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