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	Consolidated Investment Vehicles [Member]
Beginning Balance at Mar. 31, 2014			$ 11,717	$ 3,148,396	$ (29,922)	$ 29,922	$ 1,526,662	$ 37,949
Stock options exercised			67	19,618
Deferred compensation employee stock trust			4	2,063
Stock-based compensation			91	43,609
Adjustments to Additional Paid in Capital, Other				0
Employee tax withholdings by settlement of net share transactions			(47)	(21,879)
Shares repurchased and retired	$ (266,522)		(533)	(265,989)
APIC reclassified for MEP vesting	(1,816)			(1,816)
Shares Issued to plans					(2,067)	2,067
Distributions and forfeitures					1,145	(1,145)
Net Income Attributable to Legg Mason, Inc.		$ 154,121					154,121		$ 4,018
Dividends declared							(56,455)
RE Reclassified for MEP Amortization							0
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax		(4,028)						(4,028)
Reclassification for assets held for sale								(114)
Foreign currency translation adjustment		(52,790)						(52,790)
Ending Balance at Dec. 31, 2014		4,540,646	11,299	2,924,002	(30,844)	30,844	1,624,328	(18,983)
Beginning Balance at Mar. 31, 2015		4,484,901	11,147	2,844,441	(29,570)	29,570	1,690,055	(60,742)
Stock options exercised			26	8,091
Deferred compensation employee stock trust			2	377
Stock-based compensation			13	52,584
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				(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		$ (3,742)
Dividends declared							(65,781)
RE Reclassified for MEP Amortization	$ 2,489						(673)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax		4,314						4,314
Reclassification for assets held for sale								0
Foreign currency translation adjustment		(21,681)						(21,681)
Ending Balance at Dec. 31, 2015		$ 4,285,257	$ 10,770	$ 2,708,754	$ (27,321)	$ 27,321	$ 1,643,842	$ (78,109)