VIE Consolidated Income Statements Details (Details 2) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Balance Before Consolidation of CIVs
Condensed Income Statements, Captions [Line Items]
Total Operating Revenues	$ 673,168	$ 704,079	$ 1,381,903	$ 1,398,143
Total Operating Expenses	540,023	573,486	1,124,110	1,147,801
OPERATING INCOME	133,145	130,593	257,793	250,342
Total Other Non-Operating Income (Expense)	(40,988)	(121,714)	(45,867)	(128,530)
INCOME BEFORE INCOME TAX PROVISION	92,157	8,879	211,926	121,812
Income tax provision	27,647	3,804	52,737	44,460
NET INCOME	64,510	5,075	159,189	77,352
Net Income (Loss) Attributable to Noncontrolling Interest	191	178	322	267
Net Income Attributable to Legg Mason, Inc.	64,319	4,897	158,867	77,085
CIVs
Condensed Income Statements, Captions [Line Items]
Total Operating Revenues	0	0	0	0
Total Operating Expenses	115	238	220	441
OPERATING INCOME	(115)	(238)	(220)	(441)
Total Other Non-Operating Income (Expense)	(2,303)	(82)	(1,896)	2,925
INCOME BEFORE INCOME TAX PROVISION	(2,418)	(320)	(2,116)	2,484
Income tax provision	0	0	0	0
NET INCOME	(2,418)	(320)	(2,116)	2,484
Net Income (Loss) Attributable to Noncontrolling Interest	0	(392)	0	676
Net Income Attributable to Legg Mason, Inc.	(2,418)	72	(2,116)	1,808
Eliminations
Condensed Income Statements, Captions [Line Items]
Total Operating Revenues	(82)	(184)	(167)	(367)
Total Operating Expenses	(82)	(184)	(167)	(367)
OPERATING INCOME	0	0	0	0
Total Other Non-Operating Income (Expense)	827	266	785	(1,203)
INCOME BEFORE INCOME TAX PROVISION	827	266	785	(1,203)
Income tax provision	0	0	0	0
NET INCOME	827	266	785	(1,203)
Net Income (Loss) Attributable to Noncontrolling Interest	(1,591)	338	(1,331)	605
Net Income Attributable to Legg Mason, Inc.	2,418	(72)	2,116	(1,808)
Consolidated Legg Mason, Inc.
Condensed Income Statements, Captions [Line Items]
Total Operating Revenues	673,086	703,895	1,381,736	1,397,776
Total Operating Expenses	540,056	573,540	1,124,163	1,147,875
OPERATING INCOME	133,030	130,355	257,573	249,901
Total Other Non-Operating Income (Expense)	(42,464)	(121,530)	(46,978)	(126,808)
INCOME BEFORE INCOME TAX PROVISION	90,566	8,825	210,595	123,093
Income tax provision	27,647	3,804	52,737	44,460
NET INCOME	62,919	5,021	157,858	78,633
Net Income (Loss) Attributable to Noncontrolling Interest	(1,400)	124	(1,009)	1,548
Net Income Attributable to Legg Mason, Inc.	$ 64,319	$ 4,897	$ 158,867	$ 77,085