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Stock-Based Compensation (Details 3) (USD $)	9 Months Ended
Stock-Based Compensation (Details 3) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Legg Mason Group
Share-based Compensation Arrangement by Share Based Payment Award Fair Value Assumptions
Weighted-average grant date fair value, granted (in dollars per share)	$ 9.47	$ 13.13
Black-Scholes option pricing model
Share-based Compensation Arrangement by Share Based Payment Award Fair Value Assumptions
Expected dividend yield (as a percent)	1.44%	1.39%
Risk-free interest rate (as a percent)	0.81%	1.95%
Expected volatility (as a percent)	51.80%	47.16%
Expected lives	5 years 7 days	5 years 44 days

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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