Commitments, Contingencies And Guarantees (Narrative) (Details) participant in Thousands, £ in Millions	1 Months Ended		6 Months Ended
	Mar. 31, 2016	Aug. 31, 2014 USD ($)	Jun. 30, 2016 USD ($) participant	Jun. 30, 2016 GBP (£) participant	Dec. 31, 2015 USD ($)	Mar. 18, 2015 USD ($)
Commitments Contingencies And Guarantees [Line Items]
Loan commitments outstanding to clients			$ 226,600,000
Fair value of mortgage-related and other purchase commitments			$ 165,400,000
Number of individuals judgments against in litigation | participant			124	124
Estimated litigation liability						$ 50,000,000
Fair value of derivative contracts meeting the definition of a guarantee			$ 363,500,000
54 Madison [Member]
Commitments Contingencies And Guarantees [Line Items]
Maximum amount committed to invest as per agreement			225,000,000.0
Amount of contributed commitment			87,900,000
Approved unfunded commitment			41,200,000
Berkadia [Member]
Commitments Contingencies And Guarantees [Line Items]
Surety policy issued			$ 2,500,000,000
Reimbursement of losses incurred, maximum percentage			50.00%	50.00%
Aggregate amount of commercial paper outstanding			$ 1,470,000,000
Jefferies Finance [Member]
Commitments Contingencies And Guarantees [Line Items]
Maximum amount payable under guarantee			21,600,000
Line of credit commitment to associated companies, funded portion			0		$ 19,300,000
Line of credit facility commitment of Jefferies			250,000,000		$ 250,000,000
Jefferies [Member]
Commitments Contingencies And Guarantees [Line Items]
Contractual obligations | £				£ 8.1
Contractual obligation period	18 years
Jefferies [Member] | Standby Letters Of Credit [Member]
Commitments Contingencies And Guarantees [Line Items]
Letters of credit			$ 34,300,000
Expiration period maximum			1 year
Other Subsidiaries [Member]
Commitments Contingencies And Guarantees [Line Items]
Letters of credit			$ 13,700,000
Jefferies Capital Partners LLC And Its Private Equity Funds [Member]
Commitments Contingencies And Guarantees [Line Items]
Equity commitments			23,300,000
Other Investments [Member]
Commitments Contingencies And Guarantees [Line Items]
Equity commitments			25,300,000
Folger Hill Asset Management Llc [Member]
Commitments Contingencies And Guarantees [Line Items]
Revolving credit facility term		3 years
Entity line of credit facility		$ 20,000,000
Funded revolving credit facility			9,000,000
Empire Insurance Company [Member]
Commitments Contingencies And Guarantees [Line Items]
Contractual obligations			$ 26,600,000