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] 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				$ 11,147	$ 2,844,441	$ (29,570)	$ 29,570	$ 1,690,055	$ (60,742)
Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest										$ 0				$ 0
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders		$ (691)												0
Stock options exercised				26	8,091
Deferred compensation employee stock trust				2	377
Stock-based compensation				13	52,584						$ 0
Adjustments to Additional Paid in Capital, Other					9,173
Employee tax withholdings by settlement of net share transactions				(41)	(21,495)
Shares repurchased and retired		(182,978)		(377)	(182,601)
APIC reclassified for MEP vesting		(2,489)			(1,816)
Shares Issued to plans						(379)	379
Distributions and forfeitures						2,628	(2,628)
Net Income Attributable to Legg Mason, Inc.			$ 20,241					20,241
Dividends declared								(65,781)
Reclassification from Retained Earnings to Noncontrolling Interests												$ 0	$ (673)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax			4,314						4,314
Foreign currency translation adjustment			(21,681)						(21,681)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, before Tax			0						0
Ending Balance at Dec. 31, 2015			4,285,257
Stockholders' Equity Attributable to Parent			4,285,257	10,770	2,708,754	(27,321)	27,321	1,643,842	(78,109)
Stockholders' Equity Attributable to Noncontrolling Interest														0
Stockholders' Equity Attributable to Parent			4,213,563	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										$ 5,732				5,732
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders		(18,797)												(4,555)	[1]
Beginning Balance at Mar. 31, 2016			4,235,765
Stock options exercised				14	3,906
Deferred compensation employee stock trust				1	385
Stock-based compensation				41	60,567						$ 11,121
Adjustments to Additional Paid in Capital, Other					0
Employee tax withholdings by settlement of net share transactions				(36)	(11,809)
Shares repurchased and retired		$ (291,674)		(912)	(290,762)
APIC reclassified for MEP vesting					(3,632)
Shares Issued to plans						(386)	386
Distributions and forfeitures						1,663	(1,663)
Net Income Attributable to Legg Mason, Inc.			151,332					151,332
Dividends declared								(68,377)
Reclassification from Retained Earnings to Noncontrolling Interests												$ (15,500)	$ (2,629)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax			(16,483)						(16,483)
Foreign currency translation adjustment			(55,797)						(55,797)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, before Tax			2,493						2,493
Ending Balance at Dec. 31, 2016			4,000,865
Stockholders' Equity Attributable to Parent			$ 3,977,486	$ 9,809	$ 2,462,889	$ (24,986)	$ 24,986	$ 1,641,068	$ (136,280)
Stockholders' Equity Attributable to Noncontrolling Interest	[1]													$ 23,379

[1] Related to Royce management equity plan.