Earnings Per Share Schedule of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 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	107,851	112,690	108,399	113,400
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	933	1,141	1,104	1,115
Weighted Average Number of Shares Outstanding, Diluted	108,784	113,831	109,503	114,515
Net Income Attributable to Legg Mason, Inc.	$ 64,319	$ 4,897	$ 158,867	$ 77,085
Basic (in dollars per share)	$ 0.58	$ 0.04	$ 1.43	$ 0.66
Earnings Per Share, Diluted	$ 0.58	$ 0.04	$ 1.42	$ 0.66
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.	$ 64,319	$ 4,897	$ 158,867	$ 77,085
Participating Securities, Distributed and Undistributed Earnings (Loss), Diluted	1,615	142	3,951	2,054
Net Income (Loss) Available to Common Stockholders, Diluted	$ 62,704	$ 4,755	$ 154,916	$ 75,031