VIE Consolidated Income Statements Details (Details 2) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Dec. 31, 2016		Dec. 31, 2015	Dec. 31, 2016		Dec. 31, 2015
Condensed Income Statements, Captions [Line Items]
Net Income (Loss) Attributable to Noncontrolling Interest	$ 13,088		$ 16	$ 45,067		$ (993)
Consolidated Entity Excluding Variable Interest Entities (VIE) [Member]
Condensed Income Statements, Captions [Line Items]
Revenues	715,601	[1]	659,636	2,164,162	[1]	2,041,539
Total Operating Expenses	604,075	[1]	900,165	1,851,199	[1]	2,024,275
OPERATING INCOME	111,526	[1]	(240,529)	312,963	[1]	17,264
Total Other Non-Operating Income (Expense)	(20,545)	[1]	(521)	(53,063)	[1]	(46,388)
INCOME BEFORE INCOME TAX PROVISION	90,981	[1]	(241,050)	259,900	[1]	(29,124)
Income tax provision	26,441	[1]	(103,651)	71,654	[1]	(50,914)
NET INCOME	64,540	[1]	(137,399)	188,246	[1]	21,790
Net Income (Loss) Attributable to Noncontrolling Interest	13,101	[1]	1,227	36,914	[1]	1,549
Net Income Attributable to Legg Mason, Inc.	51,439	[1]	(138,626)	151,332	[1]	20,241
Variable Interest Entity, Primary Beneficiary [Member]
Condensed Income Statements, Captions [Line Items]
Revenues	0	[1]	0	0	[1]	0
Total Operating Expenses	383	[1]	116	606	[1]	336
OPERATING INCOME	(383)	[1]	(116)	(606)	[1]	(336)
Total Other Non-Operating Income (Expense)	793	[1]	(1,509)	10,444	[1]	(3,406)
INCOME BEFORE INCOME TAX PROVISION	410	[1]	(1,625)	9,838	[1]	(3,742)
Income tax provision	0	[1]	0	0	[1]	0
NET INCOME	410	[1]	(1,625)	9,838	[1]	(3,742)
Net Income (Loss) Attributable to Noncontrolling Interest	(4)	[1]	0	552	[1]	0
Net Income Attributable to Legg Mason, Inc.	414	[1]	(1,625)	9,286	[1]	(3,742)
Consolidated Legg Mason, Inc.
Condensed Income Statements, Captions [Line Items]
Revenues	715,241		659,557	2,163,776		2,041,293
Total Operating Expenses	604,075		900,202	1,851,422		2,024,365
OPERATING INCOME	111,166		(240,645)	312,354		16,928
Total Other Non-Operating Income (Expense)	(20,198)		(1,616)	(44,301)		(48,594)
INCOME BEFORE INCOME TAX PROVISION	90,968		(242,261)	268,053		(31,666)
Income tax provision	26,441		(103,651)	71,654		(50,914)
NET INCOME	64,527		(138,610)	196,399		19,248
Net Income (Loss) Attributable to Noncontrolling Interest	13,088		16	45,067		(993)
Net Income Attributable to Legg Mason, Inc.	51,439		(138,626)	151,332		20,241
Consolidation, Eliminations [Member]
Condensed Income Statements, Captions [Line Items]
Revenues	(360)		(79)	(386)		(246)
Total Operating Expenses	(383)		(79)	(383)		(246)
OPERATING INCOME	23		0	(3)		0
Total Other Non-Operating Income (Expense)	(446)		414	(1,682)		1,200
INCOME BEFORE INCOME TAX PROVISION	(423)		414	(1,685)		1,200
Income tax provision	0		0	0		0
NET INCOME	(423)		414	(1,685)		1,200
Net Income (Loss) Attributable to Noncontrolling Interest	(9)		(1,211)	7,601		(2,542)
Net Income Attributable to Legg Mason, Inc.	$ (414)		$ 1,625	$ (9,286)		$ 3,742

[1] Other represents consolidated sponsored investment products (VREs) that are not designated as CIVs.