Stock-Based Compensation (Details 2) (Legg Mason Group [Member], USD $) In Thousands, except Per Share data, unless otherwise specified	6 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Legg Mason Group [Member]
Stock based compensation disclosure
Options outstanding, beginning of period (in shares)	5,624	5,419
Granted (in shares)	966	810
Exercised (in shares)	(1)	(8)
Canceled/forfeited (in shares)	(578)	(305)
Options outstanding, end of period (in shares)	6,011	5,916
Options outstanding (in dollars per share), beginning of period	$ 57.78	$ 59.82
Granted (in dollars per share)	$ 23.72	$ 33.99
Exercised (in dollars per share)	$ 23.72	$ 25.76
Canceled/forfeited (in dollars per share)	$ 56.37	$ 47.95
Options outstanding (in dollars per share), end of period	$ 52.44	$ 56.95
Options exercisable (in shares)	3,586
Weighted-average exercise price per share of exercisable options (in dollars per share)	$ 68.60
Weighted-average remaining contractual life of exercisable options (in years)	3 years 36 days
Unvested Options, Shares	2,425
Unamortized Compensation Cost related to Unvested Options	$ 22,912
Weighted-average period over which compensation cost related to unvested options is expected to be recognized (in years)	1.8