STOCK-BASED COMPENSATION (Details 6) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
Mar. 31, 2011	Mar. 31, 2010	Mar. 31, 2009
Deferred compensation payable in shares of Legg Mason common stock
Shares held by the employee stock trust (in shares)	3,196	2,205
Deferred compensation payable in shares of Legg Mason common stock
Deferred compensation payable in shares of Legg Mason common stock
Discounts on contributions under deferred compensation arrangement, maximum (as a percent)	10.00%
Compensation expense related to deferred compensation arrangement	$ 263	$ 176	$ 322
Shares issued under deferred compensation arrangement (in shares)	77	128	125
Weighted-average fair value per share at the grant date (in dollars per share)	$ 28.38	$ 22.53	$ 39.62

The maximum discount on contributions and dividends under the deferred compensation plan.

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- Definition

Represents the weighted-average fair value per share at the grant date under a deferred compensation arrangement.

+ Details

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- Definition

Number of common stock held in a trust that has been set up specifically to accumulate stock for the sole purpose of distribution to participating employees but not yet earned.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Statement of Position (SOP)
-Number 93-6
-Paragraph 14

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- Definition

The compensation expense recognized during the period pertaining to the deferred compensation arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph 64, 65

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Principles Board Opinion (APB)
-Number 12
-Paragraph 6, 7

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- Definition

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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- Definition

The number of shares issued pursuant to the terms of the deferred compensation plan as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph 64

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph 65

+ Details

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