Fixed Assets Fixed Assets (Details 2) (Legg Mason Group, USD $) In Thousands, unless otherwise specified	12 Months Ended
Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011
Legg Mason Group
Property, Plant and Equipment
Depreciation and amortization expense included in operating income	$ 73,829	$ 74,221	$ 79,835
Accelerated Depreciation, due to Space Reduction	21,020
Accelerated depreciation due to business streamlining		$ 10,256

The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585

Name:	us-gaap_DepreciationDepletionAndAmortization
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration