Consolidated Statements of Cash Flows - USD ($)		3 Months Ended			6 Months Ended			12 Months Ended
		Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2015	Sep. 30, 2016		Sep. 30, 2015	Mar. 31, 2016
CASH FLOWS FROM INVESTING ACTIVITIES
CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES					$ (1,025,740,000)		$ 8,045,000
CASH FLOWS FROM FINANCING ACTIVITIES
Business Acquisition, Preacquisition Contingency, Amount of Settlement		$ (6,587,000)			(6,587,000)			$ (22,765,000)
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders					(10,338,000)		(364,000)
Proceeds from (Payments to) Noncontrolling Interests					(39,469,000)		33,505,000
Consolidated Legg Mason, Inc.
CASH FLOWS FROM OPERATING ACTIVITIES
Net Income		86,532,000		$ 62,919,000	131,872,000		157,858,000
Adjustments to reconcile Net Income to net cash used in operations:
Depreciation and amortization					40,342,000		27,534,000
Accretion and amortization of securities discounts and premiums, net					2,097,000		424,000
Stock-based compensation					54,981,000		37,041,000
Deferred income taxes					30,307,000		46,749,000
Other					500,000		701,000
Decrease (increase) in assets:
Investment advisory and related fees receivable					(17,298,000)		37,970,000
Net (purchases) sales of trading and other current investments					25,002,000		(12,373,000)
Other receivables					(4,030,000)		(10,884,000)
Increase (decrease) in liabilities:
Accrued compensation					(102,908,000)		(134,114,000)
Deferred compensation					22,092,000		12,123,000
Accounts payable and accrued expenses					(3,423,000)		(18,376,000)
CASH PROVIDED BY (USED IN) OPERATING ACTIVITIES					137,859,000		151,708,000
CASH FLOWS FROM INVESTING ACTIVITIES
Payments for fixed assets					(18,684,000)		(19,858,000)
Business acquisitions, net of cash acquired of $29,830					(1,009,928,000)		0
Change in restricted cash					436,000		18,438,000
CASH FLOWS FROM FINANCING ACTIVITIES
Business Acquisition, Preacquisition Contingency, Amount of Settlement		(6,587,000)		(22,765,000)	(6,587,000)		(22,765,000)
Issuance of common stock for stock-based compensation					3,709,000		6,346,000
Employee Tax Withholdings by settlement of net share transaction					(11,802,000)		(21,178,000)
Repurchase of common stock					(201,673,000)		(157,978,000)
Dividends paid					(44,103,000)		(40,383,000)
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES					129,375,000		(202,817,000)
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Income Taxes Paid, Net					11,025,000		17,125,000
CASH FLOWS FROM OPERATING ACTIVITIES
Net Income					123,706,000	[1]	159,189,000
Adjustments to reconcile Net Income to net cash used in operations:
Unrealized Gain (Loss) on Investments					(21,382,000)		39,024,000
Net (gains) losses on investments					3,391,000		(22,336,000)
Decrease (increase) in assets:
Other assets					(11,290,000)		16,892,000
Increase (decrease) in liabilities:
Other liabilities					(37,733,000)		(23,355,000)
CASH FLOWS FROM INVESTING ACTIVITIES
Cash Acquired		33,547,000		0	33,547,000		0
Proceeds from sales and maturities of investment securities					2,436,000		9,465,000
CASH FLOWS FROM FINANCING ACTIVITIES
Repayments of Lines of Credit					(40,000,000)		0
Proceeds from Issuance of Long-term Debt					500,000,000		0
Debt issuance costs					(17,639,000)		0
EFFECT OF EXCHANGE RATES ON CASH					248,000		(7,553,000)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS					(758,258,000)		(50,617,000)
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR			$ 1,329,126,000		1,329,126,000		669,552,000	669,552,000
CASH AND CASH EQUIVALENTS AT END OF YEAR		570,868,000		$ 618,935,000	570,868,000		618,935,000	1,329,126,000
Interest Paid					45,485,000		24,551,000
Proceeds from Income Tax Refunds					(754)		(2,018)
Consolidated Investment Vehicles [Member]
CASH FLOWS FROM OPERATING ACTIVITIES
Net Income					9,416,000	[1]	(2,116,000)
Adjustments to reconcile Net Income to net cash used in operations:
Net (gains) losses on investments					(8,434,000)		1,896,000
Decrease (increase) in assets:
Other assets					56,672,000		(4,925,000)
Increase (decrease) in liabilities:
Other liabilities					2,101,000		(141,000)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from (Payments to) Noncontrolling Interests					(52,530,000)		33,141,000
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR			297,000		297,000
CASH AND CASH EQUIVALENTS AT END OF YEAR		$ 2,835,000			2,835,000			297,000
Change in Input Assumptions [Member]
Adjustments to reconcile Net Income to net cash used in operations:
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability					(25,000,000)			$ (33,375,000)
Change in Input Assumptions [Member] | Consolidated Legg Mason, Inc.
Adjustments to reconcile Net Income to net cash used in operations:
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability					(25,000,000)		0
Noncontrolling Interest [Member]
CASH FLOWS FROM FINANCING ACTIVITIES
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders					(10,338,000)		(364,000)
Proceeds from (Payments to) Noncontrolling Interests					2,604,000
Noncontrolling Interest [Member] | Clarion Partners [Member]
CASH FLOWS FROM FINANCING ACTIVITIES
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders					(2,733,000)
Proceeds from (Payments to) Noncontrolling Interests					0
Consolidated Investment Vehicles [Member]
CASH FLOWS FROM FINANCING ACTIVITIES
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders					0
Proceeds from (Payments to) Noncontrolling Interests	[2]				(42,073,000)	[3]	$ 33,505,000
Management Equity Plan [Member] | Clarion Partners [Member]
Adjustments to reconcile Net Income to net cash used in operations:
Deferred Compensation Arrangement with Individual, Compensation Expense			$ 15,200,000		$ 15,200,000

[1] Other represents consolidated sponsored investment products that are not designated as CIVs.

[2] (1) Principally related to VIE and seeded investment products.

[3] (3)Includes the impact related to the adoption of updated consolidation accounting guidance further discussed in Note 2.