Consolidated Company-Sponsored Investment Funds - Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Recurring
Variable Interest Entity [Line Items]
Derivatives	$ 13,491	$ 17,079
Derivatives	19,259	14,822
Total liabilities measured at fair value	72,327	30,781
Level 1 | Recurring
Variable Interest Entity [Line Items]
Investments	183,760	216,251
Derivatives	939	1,594
Total assets measured at fair value	311,100	320,733
Derivatives	871	2,534
Total liabilities measured at fair value	31,028	11,157
Level 2 | Recurring
Variable Interest Entity [Line Items]
Investments	8,952	400,796
Derivatives	12,552	15,485
Total assets measured at fair value	1,116,370	1,585,835
Derivatives	18,388	12,288
Total liabilities measured at fair value	18,388	12,288
Level 3 | Recurring
Variable Interest Entity [Line Items]
Investments	119	142
Derivatives	0	0
Total assets measured at fair value	119	142
Derivatives	0	0
Total liabilities measured at fair value	22,911	7,336
NAV Expedient | Recurring
Variable Interest Entity [Line Items]
Investments, NAV Expedient	314	315
Consolidated company-sponsored investment funds | Recurring
Variable Interest Entity [Line Items]
Total assets measured at fair value	590,176	358,922
Total liabilities measured at fair value	9,642	7,721
Consolidated company-sponsored investment funds | Level 1 | Recurring
Variable Interest Entity [Line Items]
Total assets measured at fair value	132,554	91,822
Total liabilities measured at fair value	936	269
Consolidated company-sponsored investment funds | Level 2 | Recurring
Variable Interest Entity [Line Items]
Total assets measured at fair value	456,768	258,727
Total liabilities measured at fair value	8,706	7,452
Consolidated company-sponsored investment funds | Level 3 | Recurring
Variable Interest Entity [Line Items]
Total assets measured at fair value	854	8,373
Total liabilities measured at fair value	0	0
VIEs
Variable Interest Entity [Line Items]
Derivatives	4,833	3,410
Derivatives	4,559	3,891
VIEs | Recurring
Variable Interest Entity [Line Items]
Investments	404,624	217,840
Derivatives	4,833	3,410
Derivatives	4,559	3,891
VIEs | Level 1 | Recurring
Variable Interest Entity [Line Items]
Investments	28,270	22,149
Derivatives	139	1,486
Derivatives	835	72
VIEs | Level 2 | Recurring
Variable Interest Entity [Line Items]
Investments	375,559	187,626
Derivatives	4,694	1,924
Derivatives	3,724	3,819
VIEs | Level 3 | Recurring
Variable Interest Entity [Line Items]
Investments	795	8,065
Derivatives	0	0
Derivatives	0	0
VOEs
Variable Interest Entity [Line Items]
Derivatives	4,339	3,816
Derivatives	5,083	3,830
VOEs | Recurring
Variable Interest Entity [Line Items]
Investments	176,380	133,856
Derivatives	4,339	3,816
Derivatives	5,083	3,830
VOEs | Level 1 | Recurring
Variable Interest Entity [Line Items]
Investments	104,069	68,063
Derivatives	76	124
Derivatives	101	197
VOEs | Level 2 | Recurring
Variable Interest Entity [Line Items]
Investments	72,252	65,485
Derivatives	4,263	3,692
Derivatives	4,982	3,633
VOEs | Level 3 | Recurring
Variable Interest Entity [Line Items]
Investments	59	308
Derivatives	0	0
Derivatives	$ 0	$ 0