Consolidated Company-Sponsored Investment Funds - Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives	$ 24,224	$ 13,491
Derivatives	26,626	19,259
Total liabilities measured at fair value	71,456	72,327
Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	209,657	183,760
Derivatives	113	939
Total assets measured at fair value	336,019	311,100
Derivatives	1,126	871
Total liabilities measured at fair value	17,046	31,028
Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	19,425	8,952
Derivatives	24,111	12,552
Total assets measured at fair value	1,925,724	1,116,370
Derivatives	25,500	18,388
Total liabilities measured at fair value	25,500	18,388
Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	114	119
Derivatives	0	0
Total assets measured at fair value	114	119
Derivatives	0	0
Total liabilities measured at fair value	28,910	22,911
Company-sponsored investment funds | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	236,126	590,176
Total liabilities measured at fair value	6,055	9,642
Company-sponsored investment funds | Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	20,402	132,554
Total liabilities measured at fair value	191	936
Company-sponsored investment funds | Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	215,207	456,768
Total liabilities measured at fair value	5,864	8,706
Company-sponsored investment funds | Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	517	854
Total liabilities measured at fair value	0	0
VIEs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives	1,332	4,833
Derivatives	4,309	4,559
VIEs | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	128,941	404,624
Derivatives	1,332	4,833
Derivatives	4,309	4,559
VIEs | Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	16,924	28,270
Derivatives	245	139
Derivatives	133	835
VIEs | Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	111,541	375,559
Derivatives	1,087	4,694
Derivatives	4,176	3,724
VIEs | Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	476	795
Derivatives	0	0
Derivatives	0	0
VOEs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives	698	4,339
Derivatives	1,746	5,083
VOEs | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	105,155	176,380
Derivatives	698	4,339
Derivatives	1,746	5,083
VOEs | Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	3,185	104,069
Derivatives	48	76
Derivatives	58	101
VOEs | Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	101,929	72,252
Derivatives	650	4,263
Derivatives	1,688	4,982
VOEs | Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	41	59
Derivatives	0	0
Derivatives	$ 0	$ 0