Commitments and Contingencies Information Regarding Rental Commitments (Details 2) - USD ($) $ in Thousands		12 Months Ended
		Mar. 31, 2017	Sep. 30, 2017	Mar. 31, 2016
Property Subject to or Available for Operating Lease [Line Items]
Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals			$ 119,471
Percentage of Sublease Rentals due from Counterparty			35.00%
Operating Leases, Future Minimum Payments Due	[1]		$ 671,860
Commitments Related to Vacated and Subleased Space [Member]
Property Subject to or Available for Operating Lease [Line Items]
Valuation Allowances and Reserves, Balance		$ 28,821	29,422
Commitments Related to Vacated Space that Remains Vacant [Member]
Property Subject to or Available for Operating Lease [Line Items]
Valuation Allowances and Reserves, Balance		10,867	3,789
Operating Leases, Future Minimum Payments Due			7,558
Vacated Office Space [Member]
Property Subject to or Available for Operating Lease [Line Items]
Valuation Allowances and Reserves, Balance		39,688	$ 33,211	$ 52,240
Valuation Allowances and Reserves, Period Increase (Decrease)		(2,700)
EnTrustPermal [Member]
Property Subject to or Available for Operating Lease [Line Items]
Valuation Allowances and Reserves, Balance		9,069		$ 7,212
Valuation Allowances and Reserves, Period Increase (Decrease)		$ (4,495)

[1] (1) Includes $593,654 in real estate and equipment leases and $78,206 in service and maintenance agreements.