Changes in Level 3 Assets and Liabilities (Details 3) - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2015	Mar. 31, 2015
Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ 40,500	$ 15,911	$ 40,500	$ 15,911	$ 39,145	$ 13,021	$ 15,656	$ 23,961
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	1,442	387	28,258	1,445
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0	0	(5,352)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(713)	(45)	(1,870)	(4,394)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease)	626	(87)	1,091	251
Consolidated Entity Excluding Variable Interest Entities (VIE) [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)	7,062	2,460	29,188	(1,642)
Contingent Consideration Liability | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	52,053	90,219	52,053	90,219	62,923	84,585	92,744	110,784
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Purchases	2,000	0	2,000	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	(6,587)	0	(6,587)	(22,765)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Period Increase (Decrease)	(6,283)	(2,525)	(27,945)	2,200
Other Long-term Investments [Member] | Other Investments [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	245	77	245	77	90	83	76	77
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease)	155	1	162	0
Other Investments [Member] | Equity method investments in partnerships and Llc [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		87		87			87	7,526
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		0		(5,352)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		0		(1,821)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease)		0		(266)
Seed Capital in Proprietary Funds [Member] [Domain] | Trading Revenue [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	0	2	0	2	0	3	2	2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0	0	(3)	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease)	0	0	0	0
Long Term Incentive Compensation Plans [Member] | Equity method investments in partnerships and Llc [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	2,653		2,653		2,587	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	406		2,959
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(406)		(428)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease)	66		122
Long Term Incentive Compensation Plans [Member] | Cost-method Investments [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	7,501	7,040	7,501	7,040	7,501	7,501	6,653	5,595
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0	387	0	1,445
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease)	0	0	0	0
Proprietary Funds [Member] | Equity method investments in partnerships and Llc [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	552	634	552	634	644	627	722	734
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease)	(92)	(88)	(75)	(100)
Proprietary Funds [Member] | Cost-method Investments [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	3,827	8,071	3,827	8,071	3,810	4,807	$ 8,116	$ 10,027
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0	(45)	(1,000)	(2,573)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease)	17	$ 0	20	$ 617
Real Estate Investment [Member] | Equity method investments in partnerships and Llc [Member] | Consolidated Entity Excluding Consolidated Investment Vehicles Before Eliminations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	25,722		25,722		$ 24,513	$ 0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	1,036		25,299
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(307)		(439)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease)	$ 480		$ 862