Investments Remaining Term, Category One

No definition available.

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- Definition

Investments Remaining Term, Category Two

+ References

No definition available.

+ Details

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- Definition

Investments Remaining Term, High End of Range

+ References

No definition available.

+ Details

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- Definition

This element represents the percentage of the investment which is not subject to redemption restrictions.

+ References

No definition available.

+ Details

Name:	lm_PercentageNotSubjecttoRedemption
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- Definition

This element represents the percentage of investment having a 20 year redemption period.

+ References

No definition available.

+ Details

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- Definition

This element represents the percentage of the investment subject to monthly redemption.

+ References

No definition available.

+ Details

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- Definition

This element represents the percentage of the investment subject to quarterly redemption.

+ References

No definition available.

+ Details

Name:	lm_PercentageOfQuarterlyRedemption
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- Definition

This element represents the percentage of the investment funds that are subject to redemption (which may be monthly, quarterly, or annually) and have a remaining term of less than one year.

+ References

No definition available.

+ Details

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- Definition

This element represents the percentage of the investment subject to daily redemption.

+ References

No definition available.

+ Details

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- Definition

Fair value of investment in certain entities that calculate net asset value per share. Includes, but is not limited to, by unit, membership interest, or other ownership interest. Investment includes, but is not limited to, investment in certain hedge funds, venture capital funds, private equity funds, real estate partnerships or funds. Excludes measurement of net asset value as estimate of fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=SL6742756-110258

+ Details

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Balance Type:	debit
Period Type:	instant

- 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.

+ References

No definition available.

+ Details

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- Definition

The amount of unfunded commitments for which the entity is obligated, to those certain investments for which net asset value per share is calculated (including by unit, membership interest, or other equity (ownership interest) unit measure) (alternative investments).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=SL6742756-110258

+ Details

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- Details

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- Details

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Fair Values of Assets and Liabilities NAV Investments (Details 4) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Funds-Of-Hedge Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
PercentageDailyRedemption		1.00%
Percentage of Monthly Redemption		20.00%
Percentage of Quarterly Redemption		7.00%
Percentage Not Subject to Redemption		72.00%
Other Investments [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Percentage of Redemption, Investment Funds		26.00%
Percentage of Investment of 20 Year Redemption		74.00%
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Alternative Investment, Fair Value Disclosure		$ 41,384	$ 52,772
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments		26,514
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] \| Funds-Of-Hedge Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Alternative Investment, Fair Value Disclosure		11,122	18,537
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] \| Hedge Funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Alternative Investment, Fair Value Disclosure		6,479	10,107
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments		20,000
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] \| Private Equity Funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Alternative Investment, Fair Value Disclosure		14,377	17,612
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments		6,514
Investments Remaining Term, High End of Range	11 years
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] \| Real Estate Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Alternative Investment, Fair Value Disclosure		9,236	6,292
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] \| Other Investments [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Alternative Investment, Fair Value Disclosure		$ 170	$ 224
Investments Remaining Term, Category One	1 year
Investments Remaining Term, Category Two	14 years