Fair Values of Assets and Liabilities (Details 2) (Legg Mason, Inc., USD $) In Thousands, unless otherwise specified	12 Months Ended
	Mar. 31, 2012		Mar. 31, 2011
Quoted prices in active markets (Level 1)
Cash equivalents:
Money market funds	$ 893,738		$ 912,951
Time deposits	0		0
Total cash equivalents	893,738		912,951
Investment securities:
Trading investments relating to long-term incentive compensation plans	111,257		120,107
Trading proprietary fund products and other investments	143,002		90,123
Equity method investments relating to long-term incentive compensation plans, proprietary fund products and other investments	11,565		15,645
Total current investments	265,824		225,875
Available-for-sale investment securities	2,091		2,666
Investments in partnerships, LLCs and other	851		0
Equity method investments in partnerships and LLCs	1,415		1,420
Derivative Assets:
Currency and market hedges	84		1,169
Other investments	0		0
Financial assets measured at fair value	1,164,003		1,144,081
Derivative liabilities:
Currency and market hedges	(886)		(3,120)
Significant other observable inputs (Level 2)
Cash equivalents:
Money market funds	0		0
Time deposits	88,289		92,877
Total cash equivalents	88,289		92,877
Investment securities:
Trading investments relating to long-term incentive compensation plans	0		0
Trading proprietary fund products and other investments	79,583		102,562
Equity method investments relating to long-term incentive compensation plans, proprietary fund products and other investments	54,934		48,528
Total current investments	134,517		151,090
Available-for-sale investment securities	9,810		8,622
Investments in partnerships, LLCs and other	5,351		0
Equity method investments in partnerships and LLCs	1,348		0
Derivative Assets:
Currency and market hedges	0		0
Other investments	0		0
Financial assets measured at fair value	239,315		252,589
Derivative liabilities:
Currency and market hedges	0		0
Significant unobservable inputs (Level 3)
Cash equivalents:
Money market funds	0		0
Time deposits	0		0
Total cash equivalents	0		0
Investment securities:
Trading investments relating to long-term incentive compensation plans	0		0
Trading proprietary fund products and other investments	0		11,378
Equity method investments relating to long-term incentive compensation plans, proprietary fund products and other investments	11,778		12,167
Total current investments	11,778		23,545
Available-for-sale investment securities	12		12
Investments in partnerships, LLCs and other	28,763		22,167
Equity method investments in partnerships and LLCs	166,438		153,931
Derivative Assets:
Currency and market hedges	0		0
Other investments	112		270
Financial assets measured at fair value	207,103		199,925
Derivative liabilities:
Currency and market hedges	0		0
Total
Cash equivalents:
Money market funds	893,738	[1]	912,951	[1]
Time deposits	88,289	[1]	92,877	[1]
Total cash equivalents	982,027	[1]	1,005,828	[1]
Investment securities:
Trading investments relating to long-term incentive compensation plans	111,257	[2]	120,107	[2]
Trading proprietary fund products and other investments	222,585	[3]	204,063	[3]
Equity method investments relating to long-term incentive compensation plans, proprietary fund products and other investments	78,277	[4],[5]	76,340	[4],[5]
Total current investments	412,119		400,510
Available-for-sale investment securities	11,913		11,300
Investments in partnerships, LLCs and other	34,965		22,167
Equity method investments in partnerships and LLCs	169,201	[4]	155,351	[4]
Derivative Assets:
Currency and market hedges	84		1,169
Other investments	112		270
Financial assets measured at fair value	1,610,421		1,596,595
Derivative liabilities:
Currency and market hedges	(886)		(3,120)
Cash and Cash Equivalents, Maturity Period	90
Equity method investments relating to long-term incentive compensation plans	54,934		48,528
Equity method investments relating to proprietary fund products and other investments	$ 23,343		$ 27,812
Proprietary fund products disclosures
Proprietary fund products and other investments, equity securities percentage (as a percent)	52.00%		60.00%
Proprietary fund products and other investments, debt securities percentage (as a percent)	48.00%		40.00%

[1] Cash equivalents include highly liquid investments with original maturities of 90 days or less. Cash investments in actively traded money market funds are measured at NAV and are classified as Level 1. Cash investments in time deposits are measured at amortized cost, which approximates fair value because of the short time between the purchase of the instrument and its expected realization, and are classified as Level 2

[2] Primarily mutual funds where there is minimal market risk to the Company as any change in value is primarily offset by an adjustment to compensation expense and related deferred compensation liability

[3] Trading proprietary fund products and other investments primarily represent mutual funds that are invested approximately 52% and 48% in equity and debt securities as of March 31, 2012, respectively, and were invested approximately 60% and 40% in equity and debt securities as of March 31, 2011, respectively.

[4] Includes investments under the equity method (which approximates fair value) relating to long-term incentive compensation plans of $54,934 and $48,528 as of March 31, 2012 and March 31, 2011, respectively, and proprietary fund products and other investments of $23,343 and $27,812 as of March 31, 2012 and March 31, 2011, respectively, which are classified as Investment securities on the Consolidated Balance Sheets

[5] Substantially all of Legg Mason's equity method investments are investment companies which record their underlying investments at fair value. Fair value is measured using Legg Mason's share of the investee's underlying net income or loss, which is predominately representative of fair value adjustments in the investments held by the equity method investee