Changes in Level 3 Assets and Liabilities (Details 3) - Consolidated Entity Excluding Variable Interest Entities (VIE) [Member] - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning of Period	$ 41,918	$ 41,897
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	17,139	9,105
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(6,198)	(8,908)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease)	2,839	(176)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, End of Period	55,698	41,918	$ 41,897
Long Term Incentive Compensation Plans [Member] | Equity Method Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning of Period	0	1,337
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		39
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		(1,469)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease)		93
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, End of Period		0	1,337
Proprietary Funds [Member] | Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning of Period	1,242	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0	1,300
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease)	213	(58)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, End of Period	1,455	1,242	0
Proprietary Funds [Member] | Equity Method Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning of Period	33,725	27,661
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	9,726	7,714
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(5,211)	(4,283)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease)	2,614	2,633
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, End of Period	40,854	33,725	27,661
Other Investments [Member] | Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning of Period	6,951
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	5,263
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(2)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease)	(41)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, End of Period	12,171	6,951
Other Investments [Member] | Equity Method Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning of Period	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	2,150
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(985)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease)	53
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, End of Period	1,218	0
Other Investments [Member] | Cost-method Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning of Period	6,951	12,899
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		52
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		(3,156)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease)		(2,844)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, End of Period		6,951	12,899
Contingent Consideration Liability Fair Value [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Beginning of Period	(5,607)	(36,810)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Purchases		(1,900)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	4,870	(3,242)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Period Increase (Decrease)	(678)	29,861
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, End of Period	(1,415)	(5,607)	(36,810)
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	$ 2,876	$ 927	$ 45,099