Intangible Assets and Goodwill (Details) (Legg Mason Group, USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Mar. 31, 2012
Amortizable asset management contracts
Intangible assets
Cost	$ 205,791	$ 206,411
Accumulated amortization	(182,868)	(172,974)
Total	22,923	33,437
U.S. domestic mutual fund management contracts
Intangible assets
Indefinite-life intangible assets	2,106,351	2,502,351
Permal funds-of-hedge fund management contracts
Intangible assets
Indefinite-life intangible assets	626,000	947,000
Other fund management contracts
Intangible assets
Indefinite-life intangible assets	304,377	304,278
Trade names
Intangible assets
Indefinite-life intangible assets	52,800	69,800
Indefinite-life intangible assets
Intangible assets
Indefinite-life intangible assets	3,089,528	3,823,429
Intangible assets, net	$ 3,112,451	$ 3,856,866

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