Fair Value Disclosures (Investment in FXCM Narrative) (Details)		3 Months Ended				6 Months Ended
	Mar. 10, 2016 director	Sep. 30, 2016	Jun. 30, 2016 USD ($) $ / shares	Mar. 31, 2016	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) $ / shares	Jun. 30, 2015 USD ($)	Apr. 16, 2015 USD ($)	Jan. 31, 2015 USD ($)
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Unrealized and realized gains (losses), interest income and fees			$ 262,347,000		$ 72,238,000	$ 159,864,000	$ 801,473,000
FXCM [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Senior secured term loan receivable			$ 192,500,000			192,500,000			$ 300,000,000
Loan receivable interest rate percentage									10.00%
Increase in Interest rate per annum each quarter									1.50%
Percentage of distributions from sale of assets or certain other events until loan repayment									100.00%
Percentage of distributions from sale of assets or certain other events until next milestone amount									50.00%
Distributions milestone after loan repayment									$ 350,000,000
Percentage of distributions from sale of assets or certain other events until next milestone as a percentage of balance outstanding									90.00%
Balance outstanding used to calculate percentage of distributions from sale of assets or certain other events								$ 500,000,000
Percentage of distributions from sale of assets or certain other events thereafter									60.00%
Principal and interest payments received						16,200,000
Accrued interest rate			17.50%	16.00%
Unrealized and realized gains (losses), interest income and fees			$ (47,900,000)		$ (112,100,000)	(101,100,000)	$ 574,500,000
Investment in FXCM			$ 508,400,000			$ 508,400,000
Debt instrument, extension term	1 year
Percentage of ownership owned	49.90%
Assumed change in price of shares | $ / shares			$ 1.00			$ 1.00
Percentage of market price			12.00%			12.00%
Change in market value as a result of assumed change in price per share			$ 19,000,000			$ 19,000,000
Change in assumed volatility			10.00%			10.00%
Change in market value as a result of change in assumed volatility			$ 23,000,000			$ 23,000,000
Sensitivity analysis, estimated time to liquidity period			3 months
Change in valuation as a result of a change in estimated time to liquidity period			$ 8,000,000			$ 8,000,000
Maximum [Member] | FXCM [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Loan receivable interest rate percentage									20.50%
Balance outstanding used to calculate percentage of distributions from sale of assets or certain other events									$ 680,000,000
Minimum [Member] | FXCM [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance outstanding used to calculate percentage of distributions from sale of assets or certain other events									$ 500,000,000
Director [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Number of directors appointed | director	8
Director [Member] | FXCM [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Number of directors appointed | director	3
Director [Member] | Leucadia [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Number of directors appointed | director	3
Independent Director [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Number of directors appointed | director	2
Forecast [Member] | FXCM [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Accrued interest rate		19.00%