Variable Interest Entities and Consolidation of Investment Vehicles (Details 8) (CIVs, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Debt Instrument
Pre-defined interest rate spread of CLO debt, high end of range (as a percent)	4.00%
Pre-defined interest rate spread of CLO debt, low end of range (as a percent)	0.25%
Gain on Derivative Assets and Liabilities Recorded in Other Non-Operating Income of Consolidated Investment Vehicles	$ 54,603	$ 15,364
Loss on Derivative Assets and Liabilities Recorded in Other Non-Operating Income of Consolidated Investment Vehicles	(47,697)	(18,022)
Estimate of Fair Value, Fair Value Disclosure
Debt Instrument
Derivative assets		170
Derivative liabilities	$ (3,872)	$ (14,297)