Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Mar. 31, 2016
Other comprehensive income (loss):
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax	$ 119
Consolidated Legg Mason, Inc.
NET INCOME	63,537	$ 45,340
Other comprehensive income (loss):
Foreign currency translation adjustment	10,671	(16,183)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	0	(3,007)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax	1,708	0	$ 0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0	324
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax	1,708	0	0
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	0	(2,683)
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	0	0	3
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	0	0	(3)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, before Tax	0	(6,112)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax	119	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax	119	(6,112)
Total other comprehensive income (loss)	10,790	(24,978)
COMPREHENSIVE INCOME	74,327	20,362
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest	12,284	13,886
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Other comprehensive income (loss):
COMPREHENSIVE INCOME ATTRIBUTABLE TO LEGG MASON, INC.	62,043	6,476
AOCI Attributable to Parent [Member] | Consolidated Legg Mason, Inc.
Other comprehensive income (loss):
Foreign currency translation adjustment	10,671
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, before Tax	119	$ (6,112)
Treasury Lock [Member] | Consolidated Legg Mason, Inc.
Other comprehensive income (loss):
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax	0		(233)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax	$ 0		$ (233)