Earnings Per Share Schedule of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014
Consolidated Legg Mason, Inc.
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Weighted Average Number of Shares Outstanding, Basic	106,432	111,345	107,741	112,712
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	0	1,253	992	1,169
Weighted Average Number of Shares Outstanding, Diluted	106,432	112,598	108,733	113,881
Net Income Attributable to Legg Mason, Inc.	$ (138,626)	$ 77,036	$ 20,241	$ 154,121
Basic (in dollars per share)	$ (1.31)	$ 0.67	$ 0.17	$ 1.33
Earnings Per Share, Diluted	$ (1.31)	$ 0.67	$ 0.17	$ 1.32
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net Income Attributable to Legg Mason, Inc.	$ (138,626)	$ 77,036	$ 20,241	$ 154,121
Participating Securities, Distributed and Undistributed Earnings (Loss), Diluted	565	2,078	1,675	4,112
Net Income (Loss) Available to Common Stockholders, Diluted	$ (139,191)	$ 74,958	$ 18,566	$ 150,009