Consolidated Statements of Cash Flows - USD ($)		3 Months Ended			9 Months Ended			12 Months Ended
		Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015	Dec. 31, 2016		Dec. 31, 2015	Mar. 31, 2016
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					(18,797,000)		$ (691,000)
Proceeds from (Payments to) Noncontrolling Interests					(18,310,000)		50,571,000
Consolidated Legg Mason, Inc.
CASH FLOWS FROM OPERATING ACTIVITIES
Net Income		64,527,000		$ (138,610,000)	196,399,000		19,248,000
Adjustments to reconcile Net Income to net cash used in operations:
Depreciation and amortization					60,639,000		44,755,000
Accretion and amortization of securities discounts and premiums, net					3,058,000		2,149,000
Stock-based compensation					71,922,000		54,576,000
Deferred income taxes					59,729,000		(56,231,000)
Other					585,000		1,130,000
Decrease (increase) in assets:
Investment advisory and related fees receivable					(18,456,000)		34,892,000
Net (purchases) sales of trading and other current investments					61,935,000		(63,015,000)
Other receivables					(5,768,000)		(6,229,000)
Increase (decrease) in liabilities:
Accrued compensation					12,068,000		(48,607,000)
Deferred compensation					21,530,000		12,935,000
Accounts payable and accrued expenses					(4,689,000)		(18,770,000)
CASH PROVIDED BY (USED IN) OPERATING ACTIVITIES					346,961,000		306,392,000
CASH FLOWS FROM INVESTING ACTIVITIES
Payments for fixed assets					(27,489,000)		(29,912,000)
Business acquisitions, net of cash acquired of $29,830					(1,009,928,000)		(209,053,000)
Proceeds from Sales of Assets, Investing Activities					12,081,000		0
Change in restricted cash					4,849,000		23,734,000
CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES					(1,014,946,000)		(206,719,000)
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					4,306,000		8,496,000
Employee Tax Withholdings by settlement of net share transaction					(11,845,000)		(21,536,000)
Repurchase of common stock					(291,674,000)		(182,978,000)
Dividends paid					(66,178,000)		(62,282,000)
Proceeds from (Payments to) Noncontrolling Interests					(41,661,000)		49,880,000
CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES					28,722,000		(193,849,000)
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Income Taxes Paid, Net					14,436,000		23,644,000
Adjustments to reconcile Net Income to net cash used in operations:
Unrealized Gain (Loss) on Investments					(25,633,000)		35,002,000
Net (gains) losses on investments					959,000		(14,725,000)
Decrease (increase) in assets:
Other assets					(13,070,000)		(504,000)
Increase (decrease) in liabilities:
Other liabilities					(74,896,000)		(29,842,000)
CASH FLOWS FROM INVESTING ACTIVITIES
Cash Acquired		33,547,000		9,667,000	33,547,000		9,667,000
Proceeds from sales and maturities of investment securities					5,541,000		8,512,000
CASH FLOWS FROM FINANCING ACTIVITIES
Repayments of Lines of Credit					(40,000,000)		40,000,000
Proceeds from Issuance of Long-term Debt					500,000,000		0
Debt issuance costs					(17,639,000)		(2,664,000)
EFFECT OF EXCHANGE RATES ON CASH					(357,000)		(11,904,000)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS					(639,620,000)		(106,080,000)
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		689,506,000		$ 563,472,000	689,506,000		563,472,000	1,329,126,000
Interest Paid					59,601,000		25,015,000
Proceeds from Income Tax Refunds					(1,085)		(2,541)
Consolidated Investment Vehicles [Member]
Adjustments to reconcile Net Income to net cash used in operations:
Net (gains) losses on investments					(9,892,000)		3,406,000
Decrease (increase) in assets:
Other assets					17,530,000		(6,054,000)
Increase (decrease) in liabilities:
Other liabilities					(2,489,000)		(2,349,000)
CASH FLOWS FROM FINANCING ACTIVITIES
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR			297,000		297,000
CASH AND CASH EQUIVALENTS AT END OF YEAR		$ 1,704,000			1,704,000			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					(39,500,000)			$ (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					(39,500,000)		(26,375,000)
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]				(20,914,000)	[1]	$ 50,571,000
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] Includes the impact related to the adoption of updated consolidation accounting guidance further discussed in Note 2.

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