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, 2016	Sep. 30, 2015	Sep. 30, 2016		Sep. 30, 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	101,817	107,851	103,075		108,399
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	240	933	226		1,104
Weighted Average Number of Shares Outstanding, Diluted	102,057	108,784	103,301		109,503
Net Income Attributable to Legg Mason, Inc.	$ 66,441	$ 64,319	$ 99,893		$ 158,867
Basic (in dollars per share)	$ 0.63	$ 0.58	$ 0.94		$ 1.43
Earnings Per Share, Diluted	$ 0.63	$ 0.58	$ 0.94		$ 1.42
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.	$ 66,441	$ 64,319	$ 99,893	[1]	$ 158,867
Participating Securities, Distributed and Undistributed Earnings (Loss), Diluted	2,183	1,615	3,173		3,951
Net Income (Loss) Available to Common Stockholders, Diluted	$ 64,258	$ 62,704	$ 96,720		$ 154,916
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	3,447	2,772	3,291		2,754

[1] Other represents consolidated sponsored investment products that are not designated as CIVs.