Variable Interest Entities and Consolidation of Investment Vehicles (Details 8) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011		Mar. 31, 2011
Variable Interest Entity [Line Items]
VIE Assets Not Consolidated	$ 17,379,534		$ 21,316,932
VIE Liabilities Not Consolidated	371,361		373,465
Equity Interests on the Consolidated Balance Sheet	67,591		83,770
Maximum Risk of Loss	104,408	[1]	122,385	[1]
CDOs/CLOs
Variable Interest Entity [Line Items]
VIE Assets Not Consolidated	394,435		382,692
VIE Liabilities Not Consolidated	366,435		354,692
Equity Interests on the Consolidated Balance Sheet	0		0
Maximum Risk of Loss	449	[1]	196	[1]
Public-Private Investment Program [Member]
Variable Interest Entity [Line Items]
VIE Assets Not Consolidated	554,570		692,488
VIE Liabilities Not Consolidated	2,878		2,002
Equity Interests on the Consolidated Balance Sheet	232		290
Maximum Risk of Loss	375	[1]	290	[1]
Other sponsored investments fund [Member]
Variable Interest Entity [Line Items]
VIE Assets Not Consolidated	16,430,529		20,241,752
VIE Liabilities Not Consolidated	2,048		16,771
Equity Interests on the Consolidated Balance Sheet	67,359		83,480
Maximum Risk of Loss	$ 103,584	[1]	$ 121,899	[1]

[1] Includes equity investments the Company has made or is required to make and any earned but uncollected management fees.