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, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015
Consolidated Legg Mason, Inc.
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Weighted Average Number of Shares Outstanding, Basic	99,403	106,432	101,897	107,741
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	165	0	205	992
Weighted Average Number of Shares Outstanding, Diluted	99,568	106,432	102,102	108,733
Net Income Attributable to Legg Mason, Inc.	$ 51,439	$ (138,626)	$ 151,332	$ 20,241
Basic (in dollars per share)	$ 0.50	$ (1.31)	$ 1.44	$ 0.17
Earnings Per Share, Diluted	$ 0.50	$ (1.31)	$ 1.43	$ 0.17
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.	$ 51,439	$ (138,626)	$ 151,332	$ 20,241
Participating Securities, Distributed and Undistributed Earnings (Loss), Diluted	1,706	565	4,874	1,675
Net Income (Loss) Available to Common Stockholders, Diluted	$ 49,733	$ (139,191)	$ 146,458	$ 18,566
Restricted Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Incremental Common Shares Attributable to Participating Nonvested Shares with Non-forfeitable Dividend Rights	3,404	2,812	3,329	2,774