INVESTMENTS AND FAIR VALUES OF ASSETS AND LIABILITIES (Details 3) (Legg Mason, Inc., USD $) In Thousands	12 Months Ended
	Mar. 31, 2011	Mar. 31, 2010
Fair Value Assets and Liabilities Measured on Recurring Basis Financial Statement Unobservable Input Level 3
Assets measured at fair value using significant unobservable inputs, value at beginning of period	$ 158,030	$ 92,563
Purchases, sales, issuances and settlements, net , assets	12,672	51,995
Net transfer into/out of Level 3, assets	350
Realized and unrealized gains/(losses), net, assets	28,873	13,472
Assets measured at fair value using significant unobservable inputs, value at end of period	199,925	158,030
Total realized and unrealized gains (losses), net		34,103
Unrealized gains (losses) on Level 3 assets and liabilities still held at the reporting date	11,472	35,026
Proprietary fund products and other investments
Fair Value Assets and Liabilities Measured on Recurring Basis Financial Statement Unobservable Input Level 3
Assets measured at fair value using significant unobservable inputs, value at beginning of period	22,459	26,937
Purchases, sales, issuances and settlements, net , assets	(13,429)	(11,013)
Net transfer into/out of Level 3, assets	350
Realized and unrealized gains/(losses), net, assets	1,998	6,535
Assets measured at fair value using significant unobservable inputs, value at end of period	11,378	22,459
Equity method investments in proprietary fund products
Fair Value Assets and Liabilities Measured on Recurring Basis Financial Statement Unobservable Input Level 3
Assets measured at fair value using significant unobservable inputs, value at beginning of period	12,090	9,531
Realized and unrealized gains/(losses), net, assets	77	2,559
Assets measured at fair value using significant unobservable inputs, value at end of period	12,167	12,090
Investments in partnerships and LLCs
Fair Value Assets and Liabilities Measured on Recurring Basis Financial Statement Unobservable Input Level 3
Assets measured at fair value using significant unobservable inputs, value at beginning of period	23,049	20,630
Purchases, sales, issuances and settlements, net , assets	831	2,745
Realized and unrealized gains/(losses), net, assets	(1,713)	(326)
Assets measured at fair value using significant unobservable inputs, value at end of period	22,167	23,049
Equity method investments in partnerships and LLCs
Fair Value Assets and Liabilities Measured on Recurring Basis Financial Statement Unobservable Input Level 3
Assets measured at fair value using significant unobservable inputs, value at beginning of period	98,968	33,584
Purchases, sales, issuances and settlements, net , assets	29,335	61,042
Realized and unrealized gains/(losses), net, assets	25,628	4,342
Assets measured at fair value using significant unobservable inputs, value at end of period	153,931	98,968
Other investments
Fair Value Assets and Liabilities Measured on Recurring Basis Financial Statement Unobservable Input Level 3
Assets measured at fair value using significant unobservable inputs, value at beginning of period	1,464	1,881
Purchases, sales, issuances and settlements, net , assets	(4,065)	(779)
Realized and unrealized gains/(losses), net, assets	2,883	362
Assets measured at fair value using significant unobservable inputs, value at end of period	282	1,464
Fund support.
Fair Value Assets and Liabilities Measured on Recurring Basis Financial Statement Unobservable Input Level 3
Liabilities measured at fair value using significant unobservable inputs, value at beginning of period		(20,631)
Realized and unrealized gains/(losses), net		$ 20,631