Capital Stock (Details) (Legg Mason Group, USD $) In Thousands, except Share data, unless otherwise specified	1 Months Ended		12 Months Ended
	May 31, 2012	May 31, 2008	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2010	May 23, 2012 2.5% convertible senior notes
Common stock, authorized shares			500,000,000
Preferred stock, authorized shares			4,000,000
Shares of common stock reserved for issuance under equity plans			11,948,000	13,932,000
Common shares reserved for exchangeable shares issued in connection with acquisition					1,099,000
Stock Repurchase Program, Authorized Amount	$ 1,000,000
Common stock repurchased and retired, shares			16,199,000	13,597,000
Shares repurchased and retired, in dollars	155,000		425,475	400,266
Stock buyback authority, remaining amount (in dollars)			730,000
Proceeds from issuance of equity units (in dollars)		$ 1,150,000
Percent of interest in $1,000 principal amount of senior notes per equity unit issued (as a percent)		5.00%
Percentage of equity units exchanged (as a percent)					91.00%
Equity Units exchange				1,830,000	18,596,000
Underlying shares of common stock issuable upon exercise of warrants						14,205,000