Fair Values of Assets and Liabilities (Details 2) (Legg Mason Group, USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2011
Fair Value Assets and Liabilities Measured on Recurring Basis Financial Statement Unobservable Input Level 3
Assets measured at fair value using significant unobservable inputs, value at beginning of period	$ 169,171	$ 201,048	$ 207,103	$ 199,925
Purchases	911	660	1,123	33,096
Sales	(1,365)	(2,034)	(2,995)	(17,068)
Redemptions/Settlements/Other	(64,559)	(1,380)	(117,191)	(14,345)
Transfers Out of Level 3	(11,705)		(11,705)
Transfers, Net		0		0
Realized and unrealized gains/(losses), net	(1,634)	(8,559)	14,484	(11,873)
Assets measured at fair value using significant unobservable inputs, value at end of period	90,819	189,735	90,819	189,735
Unrealized gains (losses) on Level 3 assets and liabilities still held at the reporting date	(1,632)	(8,521)	(4,150)	(13,940)
Trading proprietary fund products and other investments
Fair Value Assets and Liabilities Measured on Recurring Basis Financial Statement Unobservable Input Level 3
Assets measured at fair value using significant unobservable inputs, value at beginning of period		179		11,378
Purchases		0		0
Sales		(165)		(11,906)
Redemptions/Settlements/Other		0		0
Transfers, Net		0		0
Realized and unrealized gains/(losses), net		(14)		528
Assets measured at fair value using significant unobservable inputs, value at end of period		0		0
Equity method investments in proprietary fund products
Fair Value Assets and Liabilities Measured on Recurring Basis Financial Statement Unobservable Input Level 3
Assets measured at fair value using significant unobservable inputs, value at beginning of period	11,705	11,605	11,778	12,167
Purchases	0	0	0	0
Sales	0	0	0	0
Redemptions/Settlements/Other	0	0	0	0
Transfers Out of Level 3	(11,705)		(11,705)
Transfers, Net		0		0
Realized and unrealized gains/(losses), net	0	(545)	(73)	(1,107)
Assets measured at fair value using significant unobservable inputs, value at end of period	0	11,060	0	11,060
Investments in partnerships, LLCs and other
Fair Value Assets and Liabilities Measured on Recurring Basis Financial Statement Unobservable Input Level 3
Assets measured at fair value using significant unobservable inputs, value at beginning of period	28,041	28,469	28,763	22,167
Purchases	0	0	0	6,932
Sales	(182)	0	(970)	0
Redemptions/Settlements/Other	(46)	(10)	(612)	(119)
Transfers Out of Level 3	0		0
Transfers, Net		0		0
Realized and unrealized gains/(losses), net	(349)	(219)	283	(740)
Assets measured at fair value using significant unobservable inputs, value at end of period	27,464	28,240	27,464	28,240
Equity method investments in partnerships and LLCs
Fair Value Assets and Liabilities Measured on Recurring Basis Financial Statement Unobservable Input Level 3
Assets measured at fair value using significant unobservable inputs, value at beginning of period	129,294	160,662	166,438	153,931
Purchases	911	660	1,123	26,164
Sales	(1,183)	(1,869)	(2,025)	(5,162)
Redemptions/Settlements/Other	(64,513)	(1,370)	(116,579)	(14,067)
Transfers Out of Level 3	0		0
Transfers, Net		0		0
Realized and unrealized gains/(losses), net	(1,273)	(7,781)	14,279	(10,564)
Assets measured at fair value using significant unobservable inputs, value at end of period	63,236	150,302	63,236	150,302
Other Investments
Fair Value Assets and Liabilities Measured on Recurring Basis Financial Statement Unobservable Input Level 3
Assets measured at fair value using significant unobservable inputs, value at beginning of period	131	133	124	282
Purchases	0	0	0	0
Sales	0	0	0	0
Redemptions/Settlements/Other	0	0	0	(159)
Transfers Out of Level 3	0		0
Transfers, Net		0		0
Realized and unrealized gains/(losses), net	(12)	0	(5)	10
Assets measured at fair value using significant unobservable inputs, value at end of period	$ 119	$ 133	$ 119	$ 133