Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands		Total	Consolidated Legg Mason, Inc.	Consolidated Legg Mason, Inc. COMMON STOCK	Consolidated Legg Mason, Inc. ADDITIONAL PAID-IN CAPITAL	Consolidated Legg Mason, Inc. EMPLOYEE STOCK TRUST	Consolidated Legg Mason, Inc. DEFERRED COMPENSATION EMPLOYEE STOCK TRUST	Consolidated Legg Mason, Inc. RETAINED EARNINGS	Consolidated Legg Mason, Inc. ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS), NET	Royce [Member]	Clarion Partners [Member]	Clarion Partners [Member] Consolidated Legg Mason, Inc. ADDITIONAL PAID-IN CAPITAL	EnTrust Capital [Member] Consolidated Legg Mason, Inc. RETAINED EARNINGS	Management Equity Plan [Member] Consolidated Legg Mason, Inc. RETAINED EARNINGS	Management Equity Plan [Member] Royce [Member]
Stockholders' Equity Attributable to Parent				$ 10,701	$ 2,693,113	$ (26,263)	$ 26,263	$ 1,576,242	$ (66,493)
Stockholders' Equity Attributable to Noncontrolling Interest	[1]														$ 22,202
Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest										$ 1,851					1,851
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders		$ (1,504)	$ 2,306												(802)	[1]
Stock options exercised				7	1,803
Deferred compensation employee stock trust				1	122
Stock-based compensation				34	25,860						$ 11,121	$ 11,121
Employee tax withholdings by settlement of net share transactions		(11,661)		(36)	(11,625)
Shares repurchased and retired		(111,673)		(347)	(111,326)
APIC reclassified for MEP vesting					(3,632)
Shares Issued to plans						(123)	123
Distributions and forfeitures						760	(760)
Net Income Attributable to Legg Mason, Inc.			33,452					33,452
Dividends declared								(23,581)
RE Reclassified for MEP Amortization		4,251						(619)
Excess Tax Benefit from Share-based Compensation, Financing Activities								0
Reclassification from Retained Earnings to Noncontrolling Interests													$ (15,500)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, before Tax			(6,112)						(6,112)
Foreign currency translation adjustment			(16,183)
Ending Balance at Jun. 30, 2016			4,117,570
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)									(2,683)
Stockholders' Equity Attributable to Parent			4,094,319	10,360	2,605,436	(25,626)	25,626	1,569,994	(91,471)
Stockholders' Equity Attributable to Noncontrolling Interest	[1]														23,251
Stockholders' Equity Attributable to Parent			3,983,374	9,573	2,385,726	(24,057)	24,057	1,694,859	(106,784)
Stockholders' Equity Attributable to Noncontrolling Interest	[1]														27,798
Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest										$ 2,261					2,261
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders		(15,913)	17,731												(1,818)	[1]
Beginning Balance at Mar. 31, 2017			4,011,172
Stock options exercised				26	7,380
Deferred compensation employee stock trust				1	125
Stock-based compensation				83	20,710							$ 0
Employee tax withholdings by settlement of net share transactions		(12,811)		(34)	(12,777)
Shares repurchased and retired		(89,649)		(237)	(89,412)
APIC reclassified for MEP vesting					0
Shares Issued to plans						(126)	126
Distributions and forfeitures						61	(61)
Net Income Attributable to Legg Mason, Inc.			50,920					50,920
Dividends declared								(27,352)
RE Reclassified for MEP Amortization		$ 1,389
Excess Tax Benefit from Share-based Compensation, Financing Activities								24,327
Reclassification from Retained Earnings to Noncontrolling Interests													$ 0	$ (1,392)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, before Tax			0						119
Foreign currency translation adjustment			10,671						10,671
Ending Balance at Jun. 30, 2017			3,994,773
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)									0
Stockholders' Equity Attributable to Parent			$ 3,966,532	$ 9,412	$ 2,311,752	$ (24,122)	$ 24,122	$ 1,741,362	$ (95,994)
Stockholders' Equity Attributable to Noncontrolling Interest	[1]														$ 28,241

[1] (2) Related to Royce management equity plan.