Fair Values of Assets and Liabilities (Details) (Legg Mason Group, USD $) In Thousands, unless otherwise specified	3 Months Ended
	Dec. 31, 2012		Mar. 31, 2012
Quoted prices in active markets (Level 1)
Cash equivalents:
Money market funds	$ 513,113		$ 893,738
Time deposits and other			0
Cash Equivalents, at Carrying Value	0
Total cash equivalents	513,113		893,738
Current investments:
Trading investments relating to long-term incentive compensation plans	100,396		111,257
Trading proprietary fund products and other investments	104,261		143,002
Equity method investments relating to long-term incentive compensation plans, proprietary fund products and other investments	12,685		11,565
Total current investments	217,342		265,824
Available-for-sale investment securities	2,031		2,091
Investments in partnerships, LLCs and other	986		851
Equity method investments in partnerships and LLCs	1,361		1,415
Derivative Assets:
Currency and market hedges	317		84
Other investments	0		0
Financial assets measured at fair value	735,150		1,164,003
Derivative liabilities:
Currency and market hedges	(744)		(886)
Significant other observable inputs (Level 2)
Cash equivalents:
Money market funds	0		0
Time deposits and other			88,289
Cash Equivalents, at Carrying Value	124,978
Total cash equivalents	124,978		88,289
Current investments:
Trading investments relating to long-term incentive compensation plans	0		0
Trading proprietary fund products and other investments	102,680		79,583
Equity method investments relating to long-term incentive compensation plans, proprietary fund products and other investments	26,294		54,934
Total current investments	128,974		134,517
Available-for-sale investment securities	10,367		9,810
Investments in partnerships, LLCs and other	2,696		5,351
Equity method investments in partnerships and LLCs	0		1,348
Derivative Assets:
Currency and market hedges	0		0
Other investments	0		0
Financial assets measured at fair value	267,015		239,315
Derivative liabilities:
Currency and market hedges	0		0
Significant unobservable inputs (Level 3)
Cash equivalents:
Money market funds	0		0
Time deposits and other			0
Cash Equivalents, at Carrying Value	0
Total cash equivalents	0		0
Current investments:
Trading investments relating to long-term incentive compensation plans	0		0
Trading proprietary fund products and other investments	0		0
Equity method investments relating to long-term incentive compensation plans, proprietary fund products and other investments	0		11,778
Total current investments	0		11,778
Available-for-sale investment securities	12		12
Investments in partnerships, LLCs and other	27,464		28,763
Equity method investments in partnerships and LLCs	63,236		166,438
Derivative Assets:
Currency and market hedges	0		0
Other investments	107		112
Financial assets measured at fair value	90,819		207,103
Derivative liabilities:
Currency and market hedges	0		0
Total
Cash equivalents:
Money market funds	513,113	[1]	893,738	[1]
Time deposits and other			88,289	[1]
Cash Equivalents, at Carrying Value	124,978	[1]
Total cash equivalents	638,091	[1]	982,027	[1]
Current investments:
Trading investments relating to long-term incentive compensation plans	100,396	[2]	111,257	[2]
Trading proprietary fund products and other investments	206,941	[3]	222,585	[3]
Equity method investments relating to long-term incentive compensation plans, proprietary fund products and other investments	38,979	[4],[5]	78,277	[4],[5]
Total current investments	346,316		412,119
Available-for-sale investment securities	12,410	[6]	11,913	[6]
Investments in partnerships, LLCs and other	31,146	[6]	34,965	[6]
Equity method investments in partnerships and LLCs	64,597	[4],[6]	169,201	[4],[6]
Derivative Assets:
Currency and market hedges	317		84
Other investments	107	[6]	112	[6]
Financial assets measured at fair value	1,092,984		1,610,421
Derivative liabilities:
Currency and market hedges	(744)		(886)
Cash and Cash Equivalents, Maturity Period	90
Proprietary fund products disclosures
Proprietary fund products and other investments, equity securities percentage (as a percent)	47.00%		52.00%
Proprietary fund products and other investments, debt securities percentage (as a percent)	53.00%		48.00%
Equity method investments relating to long-term incentive compensation plans	26,294		54,934
Equity method investments relating to proprietary fund products and other investments	$ 12,685		$ 23,343

[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 net asset value ("NAV") and are classified as Level 1. Cash investments in time deposits and other 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 47% and 53% in equity and debt securities as of December 31, 2012, respectively, and were invested approximately 52% and 48% in equity and debt securities as of March 31, 2012, respectively.

[4] 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.

[5] Includes investments under the equity method (which approximates fair value) relating to long-term incentive compensation plans of $26,294 and $54,934 as of December 31, 2012 and March 31, 2012, respectively, and proprietary fund products and other investments of $12,685 and $23,343 as of December 31, 2012 and March 31, 2012, respectively, which are classified as Investment securities on the Consolidated Balance Sheets.

[6] Amounts are included in Other non-current assets on the Consolidated Balance Sheets for each of the periods presented.