Long-Term Debt (Schedule Of Indebtedness) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Apr. 13, 2018	Dec. 31, 2017	Nov. 30, 2017
Debt Instrument [Line Items]
Long-term debt	$ 7,777,425		$ 7,777,425			$ 7,885,783
Gains (losses) recognized in Interest expense on fair value hedge	60	$ 1,537	1,692	$ 4,390
Long-term debt, fair value	$ 709,557		$ 709,557			$ 606,956
5.50% Senior Notes due October 18, 2023
Debt Instrument [Line Items]
Interest rate	5.50%		5.50%			5.50%
Principal	$ 750,000		$ 750,000			$ 750,000
6.625% Senior Notes due October 23, 2043
Debt Instrument [Line Items]
Interest rate	6.625%		6.625%			6.625%
Principal	$ 250,000		$ 250,000			$ 250,000
5.125% Senior Notes, due April 13, 2018
Debt Instrument [Line Items]
Long-term debt	0		0			$ 682,338
Interest rate					5.125%	5.125%
Principal						$ 678,300
8.50% Senior Notes, due July 15, 2019
Debt Instrument [Line Items]
Long-term debt	$ 707,072		$ 707,072			$ 728,872
Interest rate	8.50%		8.50%			8.50%
Principal	$ 680,800		$ 680,800			$ 680,800
2.375% Euro Medium Term Notes, due May 20, 2020
Debt Instrument [Line Items]
Long-term debt	$ 578,896		$ 578,896			$ 593,334
Interest rate	2.375%		2.375%			2.375%
Principal	$ 579,850		$ 579,850			$ 594,725
6.875% Senior Notes, due April 15, 2021
Debt Instrument [Line Items]
Long-term debt	$ 795,967		$ 795,967			$ 808,157
Interest rate	6.875%		6.875%			6.875%
Principal	$ 750,000		$ 750,000			$ 750,000
2.25% Euro Medium Term Notes, due July 13, 2022
Debt Instrument [Line Items]
Long-term debt	$ 4,332		$ 4,332			$ 4,389
Interest rate	2.25%		2.25%			2.25%
Principal	$ 4,639		$ 4,639			$ 4,758
5.125% Senior Notes, due January 20, 2023
Debt Instrument [Line Items]
Long-term debt	$ 613,634		$ 613,634			$ 615,703
Interest rate	5.125%		5.125%			5.125%
Principal	$ 600,000		$ 600,000			$ 600,000
4.85% Senior Notes, due January 15, 2027
Debt Instrument [Line Items]
Long-term debt	$ 712,667		$ 712,667			$ 736,357
Interest rate	4.85%		4.85%			4.85%
Principal	$ 750,000		$ 750,000			$ 750,000
6.45% Senior Debentures, due June 8, 2027
Debt Instrument [Line Items]
Long-term debt	$ 374,211		$ 374,211			$ 375,794
Interest rate	6.45%		6.45%			6.45%
Principal	$ 350,000		$ 350,000			$ 350,000
3.875% Convertible Senior Debentures, due November 1, 2029
Debt Instrument [Line Items]
Long-term debt	0		0			$ 324,779
Interest rate						3.875%
Principal						$ 324,779
4.15% Senior Notes, due January 23, 2030
Debt Instrument [Line Items]
Long-term debt	$ 987,576		$ 987,576			0
Interest rate	4.15%		4.15%
Principal	$ 1,000,000		$ 1,000,000
6.25% Senior Debentures, due January 15, 2036
Debt Instrument [Line Items]
Long-term debt	$ 511,758		$ 511,758			$ 512,040
Interest rate	6.25%		6.25%			6.25%
Principal	$ 500,000		$ 500,000			$ 500,000
6.50% Senior Notes, due January 20, 2043
Debt Instrument [Line Items]
Long-term debt	$ 420,718		$ 420,718			$ 420,990
Interest rate	6.50%		6.50%			6.50%
Principal	$ 400,000		$ 400,000			$ 400,000
Structured Notes
Debt Instrument [Line Items]
Long-term debt	709,557		709,557			614,091
Long-term debt, fair value	709,600		709,600			607,000
Foursight Capital Credit Facilities
Debt Instrument [Line Items]
Long-term debt	138,033		138,033			170,455
Other
Debt Instrument [Line Items]
Long-term debt	74,613		74,613			112,654
Parent Company
Debt Instrument [Line Items]
Long-term debt	989,913		989,913			989,021
Parent Company | 5.50% Senior Notes due October 18, 2023
Debt Instrument [Line Items]
Long-term debt	743,203		743,203			742,348
Parent Company | 6.625% Senior Notes due October 23, 2043
Debt Instrument [Line Items]
Long-term debt	246,710		246,710			246,673
Subsidiaries
Debt Instrument [Line Items]
Long-term debt	6,787,512		6,787,512			6,896,762
Jefferies Group | 5.125% Senior Notes, due April 13, 2018
Debt Instrument [Line Items]
Interest rate					5.125%
Jefferies Group | 3.875% Convertible Senior Debentures, due November 1, 2029
Debt Instrument [Line Items]
Interest rate							3.875%
Jefferies Group | Revolving Credit Facility
Debt Instrument [Line Items]
Long-term debt	158,478		158,478			0
National Beef | Reducing Revolver Loan
Debt Instrument [Line Items]
Long-term debt	0		0			120,000
National Beef | Revolving Credit Facility
Debt Instrument [Line Items]
Long-term debt	$ 0		0			$ 76,809
Interest rate swaps | Subsidiaries | 4.85% Senior Notes, due January 15, 2027
Debt Instrument [Line Items]
Gains (losses) recognized in Interest expense on fair value hedge			$ 24,100	$ (9,600)