Variable Interest Entities and Consolidation of Investment Vehicles (Details 4) (Significant unobservable inputs (Level 3), CIVs, USD $) In Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
ASSETS:
Assets measured at fair value using significant unobservable inputs, value at beginning of period	$ 55,510	$ 28,746	$ 52,151	$ 26,066
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, Sales, Issuances, Settlements		3,200		6,043
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	5,043		14,673
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	(3,871)		(15,507)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		2,627	0	2,627	[1]
Transfers of Level 3, assets	(1,057)
Realized and unrealized gains/(losses), net, assets	1,215	941	5,523	778
Assets measured at fair value using significant unobservable inputs, value at end of period	56,840	35,514	56,840	35,514
Fair Value Disclosures [Abstract]
Unrealized gains (losses) on Level 3 assets and liabilities still held at the reporting date	9,990	854	10,935	(2,084)
Hedge funds
ASSETS:
Assets measured at fair value using significant unobservable inputs, value at beginning of period	35,718	13,934	34,272	12,374
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, Sales, Issuances, Settlements		2,189		3,389
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	1,647		10,699
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	(3,871)		(15,507)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		2,627	0	2,627	[1]
Transfers of Level 3, assets	(1,057)
Realized and unrealized gains/(losses), net, assets	890	962	3,863	1,322
Assets measured at fair value using significant unobservable inputs, value at end of period	33,327	19,712	33,327	19,712
Private equity funds
ASSETS:
Assets measured at fair value using significant unobservable inputs, value at beginning of period	19,792	14,812	17,879	13,692
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases, Sales, Issuances, Settlements		1,011		2,654
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	3,396		3,974
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		0	0	0	[1]
Transfers of Level 3, assets	0
Realized and unrealized gains/(losses), net, assets	325	(21)	1,660	(544)
Assets measured at fair value using significant unobservable inputs, value at end of period	23,513	15,802	23,513	15,802
CLO debt
LIABILITIES:
Liabilities measured at fair value using significant unobservable inputs, value at beginning of period	(278,195)	(252,444)	(278,320)	0
Transfers of Level 3, liabilities		0		(249,668)	[1]
Realized and unrealized gains/(losses), net, liabilities	10,481	(378)	10,606	(3,154)
Liabilities measured at fair value using significant unobservable inputs, value at end of period	(267,714)	(252,822)	(267,714)	(252,822)
Gain (Loss) on Investments [Member]
Fair Value Disclosures [Abstract]
Fair Value Measurement with Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain (Loss) Included in Earnings	$ 11,696	$ 563	$ 16,129	$ (2,376)

[1] Transfers into Level 3 for the six months ended September 30, 2010, primarily represent liabilities recorded upon the initial consolidation of investment vehicles.