Fair Values of Assets and Liabilities by Level (Details 1) - USD ($) $ in Thousands		Sep. 30, 2017		Mar. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Proprietary Fund Products Equity Securities		72.00%		79.00%
Proprietary Fund Products Debt Securities		28.00%		21.00%
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money Market Funds, at Carrying Value	[1]	$ 322,454		$ 403,585
Time Deposits, at Carrying Value	[1]	12,179		35,835
Cash and Cash Equivalents, Fair Value Disclosure	[1]	334,633		439,420
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	[2],[3]	5,109		2,718
Other Investments	[2]	114		113
Assets, Fair Value Disclosure		812,484		948,185
Short-term Investments	[4]	394,829		423,619
Business Combination, Contingent Consideration, Liability	[5]	(21,162)		(36,810)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral		(3,167)	[2]	(4,522)	[3]
Liabilities, Fair Value Disclosure, Recurring		(24,329)		(41,332)
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money Market Funds, at Carrying Value	[1]	322,454		403,585
Time Deposits, at Carrying Value	[1]	0		0
Cash and Cash Equivalents, Fair Value Disclosure	[1]	322,454		403,585
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	[2],[3]	5,109		2,718
Other Investments	[2]	0		0
Assets, Fair Value Disclosure		637,455		737,081
Short-term Investments	[4]	309,892		330,778
Business Combination, Contingent Consideration, Liability	[5]	0		0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral		(3,167)	[2]	(4,522)	[3]
Liabilities, Fair Value Disclosure, Recurring		(3,167)		(4,522)
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money Market Funds, at Carrying Value	[1]	0		0
Time Deposits, at Carrying Value	[1]	12,179		35,835
Cash and Cash Equivalents, Fair Value Disclosure	[1]	12,179		35,835
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	[2],[3]	0		0
Other Investments	[2]	0		0
Assets, Fair Value Disclosure		84,334		116,435
Short-term Investments	[4]	72,056		80,501
Business Combination, Contingent Consideration, Liability	[5]	0		0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral		0	[2]	0	[3]
Liabilities, Fair Value Disclosure, Recurring		0		0
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money Market Funds, at Carrying Value	[1]	0		0
Time Deposits, at Carrying Value	[1]	0		0
Cash and Cash Equivalents, Fair Value Disclosure	[1]	0		0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	[2],[3]	0		0
Other Investments	[2]	114		113
Assets, Fair Value Disclosure		39,592		41,897
Short-term Investments	[4]	1,393		1,337
Business Combination, Contingent Consideration, Liability	[5]	(21,162)		(36,810)
Derivative Liability, Fair Value, Amount Not Offset Against Collateral		0	[2]	0	[3]
Liabilities, Fair Value Disclosure, Recurring		(21,162)		(36,810)
Consolidated Investment Vehicles [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Investments		104,259		49,901
Consolidated Investment Vehicles [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		90,793		33,991
Proprietary Funds [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[6]	184,278		220,673
Equity Method Investments, Fair Value Disclosure	[7]			2,502
Proprietary Funds [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[6]	110,637		141,025
Equity Method Investments, Fair Value Disclosure	[7]			0
Proprietary Funds [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[6]	69,475		75,275
Equity Method Investments, Fair Value Disclosure	[7]			2,502
Proprietary Funds [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[6]	0		0
Equity Method Investments, Fair Value Disclosure	[7]			0
Proprietary Funds [Member] | Consolidated Investment Vehicles [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		40,775		28,300
Other Investments [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[6],[8]	22,026		41,912
Other Investments [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[6],[8]	19,434		39,177
Other Investments [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[6],[8]	2,581		2,724
Other Investments [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[6],[8]	0		0
Long Term Incentive Compensation Plans [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[9]	179,924		150,903
Equity Method Investments, Fair Value Disclosure	[7]	8,601		7,629
Long Term Incentive Compensation Plans [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[9]	179,821		150,576
Equity Method Investments, Fair Value Disclosure	[7]	0		0
Long Term Incentive Compensation Plans [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[9]	0		0
Equity Method Investments, Fair Value Disclosure	[7]	0		0
Long Term Incentive Compensation Plans [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[9]	0		0
Equity Method Investments, Fair Value Disclosure	[7]	1,393		1,337
Other Long-term Investments [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investments, Fair Value Disclosure	[2],[4],[7]	13,598
Other Long-term Investments [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investments, Fair Value Disclosure	[2],[4],[7]	0
Other Long-term Investments [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investments, Fair Value Disclosure	[2],[4],[7]	0
Other Long-term Investments [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investments, Fair Value Disclosure	[2],[4],[7]	0
Other Noncurrent Assets [Member] | Proprietary Funds [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investments, Fair Value Disclosure	[2],[7]	23,497	[4]	23,464
Cost Method Investments, Fair Value Disclosure	[2]	3,371		3,440
Other Noncurrent Assets [Member] | Proprietary Funds [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investments, Fair Value Disclosure	[2],[7]	0	[4]	0
Cost Method Investments, Fair Value Disclosure	[2]	0		0
Other Noncurrent Assets [Member] | Proprietary Funds [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investments, Fair Value Disclosure	[2],[7]	0	[4]	0
Cost Method Investments, Fair Value Disclosure	[2]	0		0
Other Noncurrent Assets [Member] | Proprietary Funds [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investments, Fair Value Disclosure	[2],[7]	851	[4]	752
Cost Method Investments, Fair Value Disclosure	[2]	0		0
Other Noncurrent Assets [Member] | Real Estate Investment [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investments, Fair Value Disclosure	[2],[7]	27,382		26,909
Other Noncurrent Assets [Member] | Real Estate Investment [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investments, Fair Value Disclosure	[2],[7]	0		0
Other Noncurrent Assets [Member] | Real Estate Investment [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investments, Fair Value Disclosure	[2],[7]	0		0
Other Noncurrent Assets [Member] | Real Estate Investment [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investments, Fair Value Disclosure	[2],[7]	27,382		26,909
Other Noncurrent Assets [Member] | Other Investments [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cost Method Investments, Fair Value Disclosure	[2]	584		1,924
Other Noncurrent Assets [Member] | Other Investments [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cost Method Investments, Fair Value Disclosure	[2]	0		0
Other Noncurrent Assets [Member] | Other Investments [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cost Method Investments, Fair Value Disclosure	[2]	99		99
Other Noncurrent Assets [Member] | Other Investments [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cost Method Investments, Fair Value Disclosure	[2]	485		1,825
Other Noncurrent Assets [Member] | Long Term Incentive Compensation Plans [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cost Method Investments, Fair Value Disclosure	[2]	9,367		9,315
Other Noncurrent Assets [Member] | Long Term Incentive Compensation Plans [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cost Method Investments, Fair Value Disclosure	[2]	0		0
Other Noncurrent Assets [Member] | Long Term Incentive Compensation Plans [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cost Method Investments, Fair Value Disclosure	[2]	0		0
Other Noncurrent Assets [Member] | Long Term Incentive Compensation Plans [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cost Method Investments, Fair Value Disclosure	[2]	9,367		9,315
Other Noncurrent Assets [Member] | Other Long-term Investments [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investments, Fair Value Disclosure	[2],[7]			17,263
Other Noncurrent Assets [Member] | Other Long-term Investments [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investments, Fair Value Disclosure	[2],[7]			0
Other Noncurrent Assets [Member] | Other Long-term Investments [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investments, Fair Value Disclosure	[2],[7]			0
Other Noncurrent Assets [Member] | Other Long-term Investments [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investments, Fair Value Disclosure	[2],[7]			1,646
Consolidated Investment Vehicles [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities		6,753		26,854
Estimate of Fair Value Measurement [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money Market Funds, at Carrying Value	[1]	0		0
Time Deposits, at Carrying Value	[1]	0		0
Cash and Cash Equivalents, Fair Value Disclosure	[1]	0		0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	[2],[3]	0		0
Other Investments	[2]	0		0
Assets, Fair Value Disclosure		51,103		52,772
Short-term Investments	[4]	11,488		11,003
Business Combination, Contingent Consideration, Liability	[5]	0		0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral		0	[2]	0	[3]
Liabilities, Fair Value Disclosure, Recurring		0		0
Estimate of Fair Value Measurement [Member] | Consolidated Investment Vehicles [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[10]			24,734
Estimate of Fair Value Measurement [Member] | Hedge Funds | Consolidated Investment Vehicles [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[10]	22,465
Estimate of Fair Value Measurement [Member] | Proprietary Funds [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[6]	4,166		4,373
Equity Method Investments, Fair Value Disclosure	[7]			0
Estimate of Fair Value Measurement [Member] | Other Investments [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[6],[8]	11		11
Estimate of Fair Value Measurement [Member] | Long Term Incentive Compensation Plans [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities	[9]	103		327
Equity Method Investments, Fair Value Disclosure	[7]	7,208		6,292
Estimate of Fair Value Measurement [Member] | Other Long-term Investments [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investments, Fair Value Disclosure	[2],[4],[7]	13,598
Estimate of Fair Value Measurement [Member] | Other Noncurrent Assets [Member] | Proprietary Funds [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investments, Fair Value Disclosure	[2],[7]	22,646	[4]	22,712
Cost Method Investments, Fair Value Disclosure	[2]	3,371		3,440
Estimate of Fair Value Measurement [Member] | Other Noncurrent Assets [Member] | Real Estate Investment [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investments, Fair Value Disclosure	[2],[7]	0		0
Estimate of Fair Value Measurement [Member] | Other Noncurrent Assets [Member] | Other Investments [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cost Method Investments, Fair Value Disclosure	[2]	0		0
Estimate of Fair Value Measurement [Member] | Other Noncurrent Assets [Member] | Long Term Incentive Compensation Plans [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cost Method Investments, Fair Value Disclosure	[2]	$ 0		0
Estimate of Fair Value Measurement [Member] | Other Noncurrent Assets [Member] | Other Long-term Investments [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Method Investments, Fair Value Disclosure	[2],[7]			$ 15,617

[1] Cash equivalents include highly liquid investments with original maturities of 90 days or less. Cash investments in actively traded money market funds are classified as Level 1. Cash investments in time deposits and other are measured at amortized cost, which approximates fair value because of the short time between purchase of the instrument and its expected realization, and are classified as Level 2.

[2] Amounts are included in Other non-current assets in the Consolidated Balance Sheets for each of the periods presented.

[3] See Note 12.

[4] Excludes $40,775 and $28,300 of seed capital as of September 30, 2017, and March 31, 2017, respectively, which is related to Legg Mason's investments in CIVs. See Note 13.

[5] See Note 3 and Note 9.

[6] Trading investments of proprietary fund products and other trading investments consist of approximately 72% and 28% equity and debt securities, respectively, as of September 30, 2017, and approximately 79% and 21% equity and debt securities, respectively, as of March 31, 2017.

[7] Certain of Legg Mason's equity method investments are investment companies that record underlying investments at fair value. Therefore, the fair value of these investments is measured using Legg Mason's share of the investee's underlying net income or loss, which is predominately representative of fair value adjustments in the investments held by the equity method investee.

[8] Includes $6,753 and $26,854 in noncontrolling interests associated with consolidated seed investment products as of September 30, 2017 and March 31, 2017, respectively.

[9] Primarily mutual funds where there is minimal market risk to the Company as any change in value is primarily offset by an adjustment to compensation expense and related deferred compensation liability.

[10] Redemption restrictions: 4% daily redemption; 7% monthly redemption; 48% quarterly redemption; and 41% are subject to three to five-year lock-up or side pocket provisions.