DERIVATIVES AND HEDGING (Details) (Legg Mason, Inc., USD $) In Thousands	12 Months Ended
Mar. 31, 2011	Mar. 31, 2010
Derivative
Derivative Assets	$ 1,169	$ 697
Derivative Liabilities	3,120	485
Gains recognized on derivative instruments not designated as hedging instruments	6,718	5,964
Losses recognized on derivative instruments not designated as hedging instruments	(13,595)	(12,192)
Forward foreign currency contracts
Derivative
Open currency forward contracts with aggregate gross asset fair values	1,112	671
Open currency forward contracts with aggregate gross liability fair values	1,633	255
Forward foreign currency contracts \| Operating activities - other expense
Derivative
Gains recognized on derivative instruments not designated as hedging instruments	4,943	5,669
Losses recognized on derivative instruments not designated as hedging instruments	(6,094)	(11,092)
Forward foreign currency contracts \| Seed Capital Investments - Other non-operating income (expense)
Derivative
Gains recognized on derivative instruments not designated as hedging instruments	123	269
Losses recognized on derivative instruments not designated as hedging instruments	(355)	(19)
Futures contracts
Derivative
Cash collateral	7,099	2,185
Open futures contracts with aggregate gross asset fair values	57	26
Open futures contracts with aggregate gross liability fair values	1,487	230
Futures contracts \| Seed Capital Investments - Other non-operating income (expense)
Derivative
Gains recognized on derivative instruments not designated as hedging instruments	1,652	26
Losses recognized on derivative instruments not designated as hedging instruments	$ (7,146)	$ (1,081)

The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 44D
-Subparagraph c

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Fair value of derivative asset, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 205G

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 44C
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Fair value of derivative liability, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

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Gain included in earnings for the period from the change in fair value of derivative instruments not designated as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 45
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Loss included in earnings for the period from the change in fair value of derivative instruments not designated as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Fair value as of the balance sheet date of foreign currency derivative assets, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as assets on the balance sheet.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 107
-Paragraph 10

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Fair value as of the balance sheet date of interest rate derivative liabilities, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as liabilities on the balance sheet.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Fair value as of the balance sheet date of all price risk derivative assets not designated as hedging instruments.

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Fair value as of the balance sheet date of all price risk derivative liabilities not designated as hedging instruments.

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