Consolidated Statements of Changes in Stockholders' Equity (Consolidated Legg Mason, Inc., USD $) In Thousands, unless otherwise specified	Consolidated Legg Mason, Inc. USD ($)	Consolidated Legg Mason, Inc. Common Stock USD ($)	Consolidated Legg Mason, Inc. SHARES EXCHANGEABLE INTO COMMON STOCK USD ($)	Consolidated Legg Mason, Inc. ADDITIONAL PAID-IN CAPITAL USD ($)	Consolidated Legg Mason, Inc. EMPLOYEE STOCK TRUST USD ($)	Consolidated Legg Mason, Inc. DEFERRED COMPENSATION EMPLOYEE STOCK TRUST USD ($)	Consolidated Legg Mason, Inc. RETAINED EARNINGS USD ($)	Consolidated Legg Mason, Inc. APPROPRIATED RETAINED EARNINGS OF CONSOLIDATED INVESTMENT VEHICLE USD ($)	Consolidated Legg Mason, Inc. ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS), NET USD ($)
Balance at Mar. 31, 2009		$ 14,185	$ 3,069	$ 3,452,530	$ (35,094)	$ 35,094	$ 1,131,625	$ 0	$ (2,784)
Increase (Decrease) in Stockholders' Equity
Stock options and other stock-based compensation		8		18,758
Deferred compensation employee stock trust		13		3,156
Deferred compensation, net		66		29,056
Exchangeable shares		12	(309)	297
Equity Units exchanged		1,860		943,815
Employee tax withholdings by net share transactions		0		0
Shares repurchased and retired		0		0
Shares issued to plans					(2,938)	2,938
Distributions and forfeitures					4,937	(4,937)
Net income (loss) attributable to Legg Mason, Inc.	204,357						204,357
Dividends declared							(19,001)
Cumulative effect of change in accounting principle								0
Net income (loss) reclassified to appropriated retained earnings								0
Unrealized holding gains (losses) on investment securities, net of tax	(18)								(18)
Foreign currency translation adjustment	61,029								61,029
Balance at Mar. 31, 2010	5,841,724	16,144	2,760	4,447,612	(33,095)	33,095	1,316,981	0	58,227
Increase (Decrease) in Stockholders' Equity
Stock options and other stock-based compensation		64		31,674
Deferred compensation employee stock trust		7		2,673
Deferred compensation, net		152		34,619
Exchangeable shares		110	(2,760)	2,650
Equity Units exchanged		0		35,877
Employee tax withholdings by net share transactions		0		0
Shares repurchased and retired	(445,465)	(1,455)		(444,010)
Shares issued to plans					(2,136)	2,136
Distributions and forfeitures					765	(765)
Net income (loss) attributable to Legg Mason, Inc.	253,923						253,923
Dividends declared							(30,920)
Cumulative effect of change in accounting principle								24,666
Net income (loss) reclassified to appropriated retained earnings								(13,744)
Unrealized holding gains (losses) on investment securities, net of tax	(25)								(25)
Foreign currency translation adjustment	35,159								35,159
Balance at Mar. 31, 2011	5,770,384	15,022	0	4,111,095	(34,466)	34,466	1,539,984	10,922	93,361
Increase (Decrease) in Stockholders' Equity
Stock options and other stock-based compensation		17		16,508
Deferred compensation employee stock trust		7		2,020
Deferred compensation, net		124		32,193
Exchangeable shares		0	0	0
Equity Units exchanged		183		102,831
Employee tax withholdings by net share transactions		(6)		(1,525)
Shares repurchased and retired	(400,266)	(1,360)		(398,906)
Shares issued to plans					(2,027)	2,027
Distributions and forfeitures					4,074	(4,074)
Net income (loss) attributable to Legg Mason, Inc.	220,817						220,817
Dividends declared							(45,406)
Cumulative effect of change in accounting principle								0
Net income (loss) reclassified to appropriated retained earnings								1,299
Unrealized holding gains (losses) on investment securities, net of tax	209								209
Foreign currency translation adjustment	(22,098)								(22,098)
Balance at Mar. 31, 2012	$ 5,677,291	$ 13,987	$ 0	$ 3,864,216	$ (32,419)	$ 32,419	$ 1,715,395	$ 12,221	$ 71,472