Variable Interest Entities and Consolidation of Investment Vehicles (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Balance Before Consolidation of CIVs
Total operating revenues	$ 640,884	$ 670,522	$ 1,272,161	$ 1,388,682
Total operating expenses	560,335	562,785	1,114,858	1,179,417
Operating income (loss)	80,549	107,737	157,303	209,265
Total other non-operating income (expense)	16,763	(52,597)	(74,266)	(66,229)
Income (loss) before income tax provision (benefit)	97,312	55,140	83,037	143,036
Income tax provision (benefit)	16,397	(1,606)	11,400	26,261
Net income (loss)	80,915	56,746	71,637	116,775
Less: Net income (loss) attributable to noncontrolling interests	118	82	298	159
Net income (loss) attributable to Legg Mason, Inc.	80,797	56,664	71,339	116,616
CIVs
Total operating revenues	0	0	0	0
Total operating expenses	815	885	1,492	2,047
Operating income (loss)	(815)	(885)	(1,492)	(2,047)
Total other non-operating income (expense)	1,503	3,081	(2,632)	8,183
Income (loss) before income tax provision (benefit)	688	2,196	(4,124)	6,136
Income tax provision (benefit)	0	0	0	0
Net income (loss)	688	2,196	(4,124)	6,136
Less: Net income (loss) attributable to noncontrolling interests	0	0	0	0
Net income (loss) attributable to Legg Mason, Inc.	688	2,196	(4,124)	6,136
Eliminations
Total operating revenues	(589)	(625)	(1,174)	(1,677)
Total operating expenses	(589)	(625)	(1,174)	(1,677)
Operating income (loss)	0	0	0	0
Total other non-operating income (expense)	(508)	(1,559)	598	(3,830)
Income (loss) before income tax provision (benefit)	(508)	(1,559)	598	(3,830)
Income tax provision (benefit)	0	0	0	0
Net income (loss)	(508)	(1,559)	598	(3,830)
Less: Net income (loss) attributable to noncontrolling interests	180	637	(3,526)	2,306
Net income (loss) attributable to Legg Mason, Inc.	(688)	(2,196)	4,124	(6,136)
As Reported
Total operating revenues	640,295	669,897	1,270,987	1,387,005
Total operating expenses	560,561	563,045	1,115,176	1,179,787
Operating income (loss)	79,734	106,852	155,811	207,218
Total other non-operating income (expense)	17,758	(51,075)	(76,300)	(61,876)
Income (loss) before income tax provision (benefit)	97,492	55,777	79,511	145,342
Income tax provision (benefit)	16,397	(1,606)	11,400	26,261
Net income (loss)	81,095	57,383	68,111	119,081
Less: Net income (loss) attributable to noncontrolling interests	298	719	(3,228)	2,465
Net income (loss) attributable to Legg Mason, Inc.	$ 80,797	$ 56,664	$ 71,339	$ 116,616