Fixed Assets (Details) (Legg Mason, Inc., USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Mar. 31, 2013
Fixed assets:
Total cost	$ 599,850	$ 602,064
Less: accumulated depreciation and amortization	(404,720)	(400,245)
Fixed assets, net	195,130	201,819
Equipment
Fixed assets:
Total cost	150,385	152,065
Software
Fixed assets:
Total cost	234,947	227,739
Leasehold improvements
Fixed assets:
Total cost	$ 214,518	$ 222,260