Stock-Based Compensation Other Information (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended	15 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2015	Sep. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award
Allocated Share-based Compensation Expense	$ 66,245	$ 66,488	$ 58,983
Aggregate Cost of Awards					1,850lm_AggregateCostofAwards
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost	1,000
Rabbi trust [Domain]
Share-based Compensation Arrangement by Share-based Payment Award
Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Purchase Date				10.00%
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	283			283
Allocated Share-based Compensation Expense	$ 201	$ 160	$ 165
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted	44	51	71
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	$ 45.83	$ 31.90	$ 23.07	$ 45.83
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	660	672	726	660

The aggregate cost of the award is based on individual valuations

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Amount of capitalized and expensed compensation cost from equity-based compensation arrangements.

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Discount rate from fair value on purchase date that participants pay for shares.

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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Net number of non-option equity instruments granted to participants.

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Number of options outstanding, including both vested and non-vested options.

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