Intangible Assets and Goodwill (Details) (Legg Mason Group [Member], USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Mar. 31, 2012
Amortizable asset management contracts
Intangible assets
Cost	$ 205,880	$ 206,411
Accumulated amortization	(179,452)	(172,974)
Total	26,428	33,437
Fund management contracts
Intangible assets
Indefinite-life intangible assets	3,753,688	3,753,629
Trade names
Intangible assets
Indefinite-life intangible assets	69,800	69,800
Indefinite-life intangible assets
Intangible assets
Indefinite-life intangible assets	3,823,488	3,823,429
Intangible assets, net	$ 3,849,916	$ 3,856,866

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Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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Carrying amount of assets (excluding financial assets) that lack physical substance, excluding goodwill, having a projected indefinite period of benefit.

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Sum of the carrying amounts of all intangible assets, excluding goodwill, as of the balance sheet date, net of accumulated amortization and impairment charges.

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