Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
OTHER NON-OPERATING INCOME (EXPENSE)
Net Income (Loss) Attributable to Noncontrolling Interest	$ 11,960	$ 20,091	$ 24,577	$ 31,979
Consolidated Legg Mason, Inc.
OPERATING REVENUES
Distribution and service fees	80,668	94,545	159,574	185,927
Other	686	1,448	1,811	2,456
Revenues	768,338	748,370	1,562,180	1,448,535
OPERATING EXPENSES
Compensation and benefits	367,951	368,330	781,258	726,955
Distribution and servicing	123,634	128,868	245,983	253,531
Communications and technology	51,299	51,281	101,602	104,013
Occupancy	25,171	30,558	49,579	63,700
Amortization of intangible assets	6,082	6,271	12,421	11,974
Impairment of Intangible Assets	0	0
Impairment of Intangible Assets, Indefinite-lived (Excluding Goodwill)			34,000	0
Contingent consideration fair value adjustments	0	(7,000)	(16,550)	(25,000)
Other	49,782	42,429	102,263	112,174
Total Operating Expenses	623,919	620,737	1,310,556	1,247,347
OPERATING INCOME	144,419	127,633	251,624	201,188
OTHER NON-OPERATING INCOME (EXPENSE)
Interest income	1,572	1,545	3,040	3,393
Interest expense	(29,077)	(27,925)	(58,343)	(52,490)
Other income (expense), net	7,289	9,975	18,677	16,560
Total Other Non-Operating Income (Expense)	(18,122)	(11,199)	(33,535)	(24,103)
INCOME BEFORE INCOME TAX PROVISION	126,297	116,434	218,089	177,085
Income tax provision	38,673	29,902	66,928	45,213
NET INCOME	87,624	86,532	151,161	131,872
Net Income (Loss) Attributable to Noncontrolling Interest	11,960	20,091	24,577	31,979
NET INCOME ATTRIBUTABLE TO LEGG MASON, INC.	$ 75,664	$ 66,441	$ 126,584	$ 99,893
NET INCOME PER SHARE ATTRIBUTABLE TO LEGG MASON, INC. COMMON SHAREHOLDERS
Basic (in dollars per share)	$ 0.78	$ 0.63	$ 1.30	$ 0.94
Diluted (in dollars per share)	0.78	0.63	1.29	0.94
Common Stock, Dividends, Per Share, Declared	$ 0.28	$ 0.22	$ 0.56	$ 0.44
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
OTHER NON-OPERATING INCOME (EXPENSE)
NET INCOME ATTRIBUTABLE TO LEGG MASON, INC.	$ 75,664	$ 66,441	$ 126,584	$ 99,893
Consolidated Investment Vehicles [Member]
OTHER NON-OPERATING INCOME (EXPENSE)
Other income (expense), net	2,094	5,206	3,091	8,434
Separate Accounts [Member] | Consolidated Legg Mason, Inc.
OPERATING REVENUES
Investment Advisory Fees	253,128	233,328	503,174	460,181
Mutual Funds [Member] | Consolidated Legg Mason, Inc.
OPERATING REVENUES
Investment Advisory Fees	393,035	377,079	775,263	740,542
Performance Fees [Member] | Consolidated Legg Mason, Inc.
OPERATING REVENUES
Investment Advisory Fees	$ 40,821	$ 41,970	$ 122,358	$ 59,429