Variable Interest Entities and Consolidation of Investment Vehicles (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Balance Before Consolidation of CIVs
Total operating revenues	$ 631,277	$ 718,160
Total operating expenses	554,523	616,632
Operating income (loss)	76,754	101,528
Total other non-operating income (expense)	(91,029)	(13,632)
Income (loss) before income tax provision (benefit)	(14,275)	87,896
Income tax provision (benefit)	(4,997)	27,867
Net income (loss)	(9,278)	60,029
Less: Net income (loss) attributable to noncontrolling interests	180	77
Net income (loss) attributable to Legg Mason, Inc.	(9,458)	59,952
CIVs
Total operating revenues	0	0
Total operating expenses	677	1,163
Operating income (loss)	(677)	(1,163)
Total other non-operating income (expense)	(4,134)	5,102
Income (loss) before income tax provision (benefit)	(4,811)	3,939
Income tax provision (benefit)	0	0
Net income (loss)	(4,811)	3,939
Less: Net income (loss) attributable to noncontrolling interests	0	0
Net income (loss) attributable to Legg Mason, Inc.	(4,811)	3,939
Eliminations
Total operating revenues	(585)	(1,052)
Total operating expenses	(585)	(1,053)
Operating income (loss)	0	1
Total other non-operating income (expense)	1,105	(2,271)
Income (loss) before income tax provision (benefit)	1,105	(2,270)
Income tax provision (benefit)	0	0
Net income (loss)	1,105	(2,270)
Less: Net income (loss) attributable to noncontrolling interests	(3,706)	1,669
Net income (loss) attributable to Legg Mason, Inc.	4,811	(3,939)
As Reported
Total operating revenues	630,692	717,108
Total operating expenses	554,615	616,742
Operating income (loss)	76,077	100,366
Total other non-operating income (expense)	(94,058)	(10,801)
Income (loss) before income tax provision (benefit)	(17,981)	89,565
Income tax provision (benefit)	(4,997)	27,867
Net income (loss)	(12,984)	61,698
Less: Net income (loss) attributable to noncontrolling interests	(3,526)	1,746
Net income (loss) attributable to Legg Mason, Inc.	$ (9,458)	$ 59,952