VIE Consolidated Balance Sheet Detail (Details) - USD ($) $ in Thousands		Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Mar. 31, 2016
Variable Interest Entity
REDEEMABLE NONCONTROLLING INTERESTS		$ 698,774	$ 677,772	$ 676,164	$ 175,785
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity
Current Assets	[1]	114,854	77,406
Non-current Assets	[1]	9,536	9,987
TOTAL ASSETS	[1]	124,390	87,393
Current Liabilities	[1]	636	736
Non-current Liabilities	[1]	0	0
TOTAL LIABILITIES	[1]	636	736
REDEEMABLE NONCONTROLLING INTERESTS	[1]	6,753	26,853
Total Stockholders' Equity	[1]	117,001	59,804
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	[1]	124,390	87,393
Consolidated Entity Excluding Variable Interest Entities (VIE) [Member]
Variable Interest Entity
Current Assets	[1]	1,674,466	1,749,959
Non-current Assets	[1]	6,437,584	6,481,376
TOTAL ASSETS	[1]	8,112,050	8,231,335
Current Liabilities	[1]	698,382	808,664
Non-current Liabilities	[1]	2,803,676	2,792,084
TOTAL LIABILITIES	[1]	3,502,058	3,600,748
REDEEMABLE NONCONTROLLING INTERESTS	[1]	615,795	619,302
Total Stockholders' Equity	[1]	3,994,197	4,011,285
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	[1]	8,112,050	8,231,335
Consolidated Legg Mason, Inc.
Variable Interest Entity
Current Assets		1,751,556	1,801,747
Non-current Assets		6,444,109	6,488,668
TOTAL ASSETS		8,195,665	8,290,415
Current Liabilities		699,018	809,387
Non-current Liabilities		2,803,676	2,792,084
TOTAL LIABILITIES		3,502,694	3,601,471
REDEEMABLE NONCONTROLLING INTERESTS		698,774	677,772
Total Stockholders' Equity		3,994,197	4,011,172	$ 4,082,733
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY		8,195,665	8,290,415
Consolidation, Eliminations [Member]
Variable Interest Entity
Current Assets		(37,764)	(25,618)
Non-current Assets		(3,011)	(2,695)
TOTAL ASSETS		(40,775)	(28,313)
Current Liabilities		0	(13)
Non-current Liabilities		0	0
TOTAL LIABILITIES		0	(13)
REDEEMABLE NONCONTROLLING INTERESTS		76,226	31,617
Total Stockholders' Equity		(117,001)	(59,917)
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY		$ (40,775)	$ (28,313)

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