Noncontrolling Interests Rollforward (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Mar. 31, 2017	May 02, 2016	Mar. 31, 2016
Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Carrying Amount		$ 698,774	$ 676,164	$ 698,774	$ 676,164	$ 677,772		$ 175,785
Net Income (Loss) Attributable to Redeemable Noncontrolling Interest		9,930	18,235	20,286	28,272
Proceeds from (Payments to) Noncontrolling Interests				19,624	(39,469)
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders				(23,013)	(10,338)
Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value			510,500		510,500
Noncontrolling Interest, Period Increase (Decrease), Foreign Exchange				1,810	(59)
RE Reclassified for MEP Amortization				2,295	5,353
CIVs and Other
Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Carrying Amount	[1]	82,979	60,229	82,979	60,229	58,470		94,136
Net Income (Loss) Attributable to Redeemable Noncontrolling Interest	[1]			2,192	8,166
Proceeds from (Payments to) Noncontrolling Interests	[1],[2]			22,317	(42,073)
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders				0	0
RE Reclassified for MEP Amortization	[1]			0	0
Noncontrolling Interest [Member]
Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Carrying Amount		586,195	591,735	586,195	591,735	591,254		68,922
Net Income (Loss) Attributable to Redeemable Noncontrolling Interest				18,094	20,106
Proceeds from (Payments to) Noncontrolling Interests		(2,693)		(2,693)	2,604
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders				(23,013)	10,338
Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value			510,500		510,500
Noncontrolling Interest, Period Increase (Decrease), Foreign Exchange				1,810	(59)
RE Reclassified for MEP Amortization					0
Noncontrolling Interest, Change in Redemption Value				743
Management Equity Plan [Member]
Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Carrying Amount		29,600	24,200	29,600	24,200	28,048		12,727
Net Income (Loss) Attributable to Redeemable Noncontrolling Interest				0	0
Proceeds from (Payments to) Noncontrolling Interests					6,120
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders				0	0
RE Reclassified for MEP Amortization				1,552	5,353
EnTrustPermal [Member]
Noncontrolling Interest [Line Items]
Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value							$ 403,200
EnTrustPermal [Member] | Noncontrolling Interest [Member]
Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Carrying Amount		403,797	409,404	403,797	409,404	404,852		0
Net Income (Loss) Attributable to Redeemable Noncontrolling Interest				9,471	10,740
Proceeds from (Payments to) Noncontrolling Interests		0			0
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders				(10,526)	4,536
Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value			403,200		403,200
Noncontrolling Interest, Period Increase (Decrease), Foreign Exchange				0	0
Noncontrolling Interest, Change in Redemption Value				0
Clarion Partners [Member] | Noncontrolling Interest [Member]
Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Carrying Amount		110,889	108,205	110,889	108,205	113,173		0
Net Income (Loss) Attributable to Redeemable Noncontrolling Interest				6,434	5,638
Proceeds from (Payments to) Noncontrolling Interests		0			0
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders				(9,461)	2,733
Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value			105,300		105,300
Noncontrolling Interest, Period Increase (Decrease), Foreign Exchange				0	0
Noncontrolling Interest, Change in Redemption Value				743
RARE Infrastructure, Ltd [Member] | Noncontrolling Interest [Member]
Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Carrying Amount		69,862	67,757	69,862	67,757	68,747		67,155
Net Income (Loss) Attributable to Redeemable Noncontrolling Interest				2,206	3,364
Proceeds from (Payments to) Noncontrolling Interests		0			0
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders				(2,901)	2,703
Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value			0		0
Noncontrolling Interest, Period Increase (Decrease), Foreign Exchange				1,810	(59)
Noncontrolling Interest, Change in Redemption Value				0
Royce [Member]
Noncontrolling Interest [Line Items]
Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest		2,030	1,856	4,291	3,707
Management Equity Plan [Member] | Royce [Member]
Noncontrolling Interest [Line Items]
Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest				4,291	3,707
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders	[3]			(4,063)	(2,723)
Stockholders' Equity Attributable to Noncontrolling Interest	[3]	28,026	23,186	28,026	23,186	27,798		22,202
Other Affiliates [Member] | Noncontrolling Interest [Member]
Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Carrying Amount		1,647	6,369	1,647	6,369	$ 4,482		$ 1,767
Net Income (Loss) Attributable to Redeemable Noncontrolling Interest				(17)	364
Proceeds from (Payments to) Noncontrolling Interests		$ (2,693)			2,604
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders				(125)	366
Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value			$ 2,000		2,000
Noncontrolling Interest, Period Increase (Decrease), Foreign Exchange				0	$ 0
Noncontrolling Interest, Change in Redemption Value				$ 0

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

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

[3] (2) Related to Royce management equity plan.