Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015
OPERATING EXPENSES
Impairment of Intangible Assets, Indefinite-lived (Excluding Goodwill)		$ 371,000
OTHER NON-OPERATING INCOME (EXPENSE)
Net Income (Loss) Attributable to Noncontrolling Interest	$ 13,088	16	$ 45,067	$ (993)
Consolidated Legg Mason, Inc.
OPERATING REVENUES
Distribution and service fees	90,195	95,919	276,122	292,381
Other	1,249	461	3,705	1,705
Revenues	715,241	659,557	2,163,776	2,041,293
OPERATING EXPENSES
Compensation and benefits	327,862	282,770	1,054,817	880,255
Distribution and servicing	123,191	132,860	376,722	421,078
Communications and technology	52,630	48,509	156,643	147,031
Occupancy	23,537	35,750	87,237	87,453
Amortization of intangible assets	7,277	1,580	19,251	2,907
Impairment of Intangible Assets, Indefinite-lived (Excluding Goodwill)	35,000	371,000	35,000	371,000
Other	34,578	27,733	121,752	114,641
Total Operating Expenses	604,075	900,202	1,851,422	2,024,365
OPERATING INCOME	111,166	(240,645)	312,354	16,928
OTHER NON-OPERATING INCOME (EXPENSE)
Interest income	1,713	1,377	5,106	3,923
Interest expense	(29,495)	(8,003)	(81,985)	(33,232)
Other income (expense), net	6,126	6,520	22,686	(15,879)
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)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	26,922	(142,455)	126,612	1,881
NET INCOME ATTRIBUTABLE TO LEGG MASON, INC.	$ 51,439	$ (138,626)	$ 151,332	$ 20,241
NET INCOME PER SHARE ATTRIBUTABLE TO LEGG MASON, INC. COMMON SHAREHOLDERS
Basic (in dollars per share)	$ 0.50	$ (1.31)	$ 1.44	$ 0.17
Diluted (in dollars per share)	0.50	(1.31)	1.43	0.17
Common Stock, Dividends, Per Share, Declared	$ 0.22	$ 0.20	$ 0.66	$ 0.60
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
OTHER NON-OPERATING INCOME (EXPENSE)
NET INCOME ATTRIBUTABLE TO LEGG MASON, INC.	$ 51,439	$ (138,626)	$ 151,332	$ 20,241
Consolidated Investment Vehicles [Member]
OTHER NON-OPERATING INCOME (EXPENSE)
Other income (expense), net	1,458	(1,510)	9,892	(3,406)
Separate Accounts [Member] | Consolidated Legg Mason, Inc.
OPERATING REVENUES
Investment Advisory Fees	231,922	208,501	692,103	621,760
Mutual Funds [Member] | Consolidated Legg Mason, Inc.
OPERATING REVENUES
Investment Advisory Fees	368,962	345,501	1,109,504	1,089,717
Performance Fees [Member] | Consolidated Legg Mason, Inc.
OPERATING REVENUES
Investment Advisory Fees	$ 22,913	$ 9,175	$ 82,342	$ 35,730