Consolidated Company-Sponsored Investment Funds - Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives	$ 26,670	$ 13,491
Derivatives	28,230	19,259
Total liabilities measured at fair value	71,936	72,327
Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	162,159	183,760
Derivatives	317	939
Total assets measured at fair value	294,090	311,100
Derivatives	223	871
Total liabilities measured at fair value	14,206	31,028
Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	22,096	8,952
Derivatives	26,353	12,552
Total assets measured at fair value	1,917,340	1,116,370
Derivatives	28,007	18,388
Total liabilities measured at fair value	28,007	18,388
Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	121	119
Derivatives	0	0
Total assets measured at fair value	121	119
Derivatives	0	0
Total liabilities measured at fair value	29,723	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	233,049	590,176
Total liabilities measured at fair value	5,546	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	19,387	132,554
Total liabilities measured at fair value	300	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	213,065	456,768
Total liabilities measured at fair value	5,246	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	597	854
Total liabilities measured at fair value	0	0
VIEs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives	1,299	4,833
Derivatives	4,391	4,559
VIEs | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	137,727	404,624
Derivatives	1,299	4,833
Derivatives	4,391	4,559
VIEs | Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	17,386	28,270
Derivatives	199	139
Derivatives	284	835
VIEs | Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	119,822	375,559
Derivatives	1,100	4,694
Derivatives	4,107	3,724
VIEs | Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	519	795
Derivatives	0	0
Derivatives	0	0
VOEs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives	3,574	4,339
Derivatives	1,155	5,083
VOEs | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	90,449	176,380
Derivatives	3,574	4,339
Derivatives	1,155	5,083
VOEs | Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	1,791	104,069
Derivatives	11	76
Derivatives	16	101
VOEs | Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	88,580	72,252
Derivatives	3,563	4,263
Derivatives	1,139	4,982
VOEs | Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	78	59
Derivatives	0	0
Derivatives	$ 0	$ 0