Fair Values of Assets and Liabilities (Details) (Fair Value, Disclosure Item Amounts, Legg Mason Group, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Mar. 31, 2011
Fair Value, Disclosure Item Amounts | Legg Mason Group
Investment securities:
Current investments	$ 371,080		$ 412,119
Available-for-sale investments	12,400		11,913
Other	99	[1]	112	[1]
Total	383,579		424,144
Net unrealized and realized gain (loss) for investment securities classified as trading	18,260		(6,063)		28,355
Available-for-sale:
Proceeds	5,272		6,197		4,012
Gross realized gains	22		6		7
Gross realized losses	43		25		19
Gross unrealized gains for investments classified as available-for-sale	230		551
Gross unrealized losses for investments classified as available-for-sale	$ (188)		$ (184)

[1] Includes investments in private equity securities that do not have readily determinable fair values.