Consolidated Balance Sheets - USD ($) $ in Thousands		Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Receivables:
Fixed assets, net		$ 150,230	$ 148,406
Current Liabilities
Short-term borrowings			125,500
Long-term Debt, Current Maturities		250,636	0
Long-term debt, net		1,971,131	2,221,810
REDEEMABLE NONCONTROLLING INTERESTS		$ 676,950	$ 732,295	$ 727,706
STOCKHOLDERS' EQUITY
Common Stock, Par or Stated Value Per Share		$ 0.10	$ 0.10
Common Stock, Shares Authorized		500,000,000	500,000,000
Common Stock, Shares, Issued		85,533,667	84,606,408
Defined Benefit Plan, Funded (Unfunded) Status of Plan		$ 28,227	$ 34,940
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Current Assets
Cash and Cash Equivalents		835,168	736,130	680,322
Restricted Cash and Cash Equivalents, Current		22,336	30,428	17,605
Receivables:
Investment securities	[1]	331,588	399,370
Other current assets		76,185	65,010
Other non-current assets		149,563	134,407
Current Liabilities
Other current liabilities		93,050	204,264
Consolidated Investment Vehicles [Member]
Current Assets
Cash and Cash Equivalents		3,528	2,800	4,325
Receivables:
Investment securities		142,337	140,133
Other current assets		5,873	1,893
Other non-current assets		10,668	9,257
Current Liabilities
Other current liabilities		11,351	634
Consolidated Legg Mason, Inc.
Receivables:
Investment advisory and related fees		432,607	475,594
Other receivables		61,396	77,024
Total Current Assets		1,911,018	1,928,382
Fixed assets, net		150,230	148,406
Intangible assets, net		3,389,799	3,797,659
Goodwill		1,881,470	1,932,355
Deferred income taxes		189,867	202,068
TOTAL ASSETS		7,682,615	8,152,534
Current Liabilities
Accrued compensation		522,363	476,061
Accounts Payable and Accrued Liabilities, Current		203,881	175,583
Short-term borrowings			125,500
Total Current Liabilities		1,081,281	982,042
Deferred compensation		81,957	92,422
Deferred income taxes		99,544	139,787
Business Combination, Contingent Consideration, Liability, Noncurrent		1,350	1,900
Other non-current liabilities		119,069	132,042
Long-term debt, net		1,971,131	2,221,810
TOTAL LIABILITIES		3,352,982	3,568,103
REDEEMABLE NONCONTROLLING INTERESTS		676,950	732,295
STOCKHOLDERS' EQUITY
Common stock, par value $.10; authorized 500,000,000 shares; issued 85,533,667 shares for December 31, 2018 and 84,606,408 shares for March 31, 2017		8,553	8,461
Additional paid-in capital		2,028,586	1,976,364
Employee stock trust		(21,383)	(21,996)
Deferred compensation employee stock trust		21,383	21,996
Retained earnings		1,723,817	1,894,762
AOCI Including Portion Attributable to Noncontrolling Interest, before Tax		(135,767)	(55,182)
TOTAL STOCKHOLDERS' EQUITY		3,652,683	3,852,136	3,833,492
Stockholders' Equity Attributable to Parent		3,625,189	3,824,405	3,805,831
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY		7,682,615	8,152,534
Management Equity Plan [Member] | Royce [Member]
STOCKHOLDERS' EQUITY
Stockholders' Equity Attributable to Noncontrolling Interest		27,494	27,731	$ 27,661
Fair Value, Inputs, Level 3 [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Receivables:
Investment securities	[1]	$ 1,266	$ 1,242

[1] Excludes $71,564 and $43,854 of seed capital as of December 31, 2018 and March 31, 2018, respectively, which is related to Legg Mason's investments in CIVs. See Note 13.