Variable Interest Entities and Consolidation of Investment Vehicles (Details 4) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Mar. 31, 2012
Consolidated Legg Mason, Inc. | Minimum
Unobservable input subject to measurement uncertainty
Discount rate	1.50%
Default rate	2.50%
Consolidated Legg Mason, Inc. | Maximum
Unobservable input subject to measurement uncertainty
Discount rate	22.30%
Default rate	4.00%
Consolidated Legg Mason, Inc. | Weighted-average
Unobservable input subject to measurement uncertainty
Discount rate	3.40%
Default rate	3.40%
Constant prepayment rate	15.00%
Estimate of Fair Value, Fair Value Disclosure | CIVs
Assets measured at fair value using significant unobservable inputs subject to measurement uncertainty
CLO debt	$ (273,560)	$ (271,707)