Consolidated Company-Sponsored Investment Funds - Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Recurring
Variable Interest Entity [Line Items]
Derivatives	$ 21,741	$ 13,491
Derivatives	30,537	19,259
Total liabilities measured at fair value	76,078	72,327
Level 1 | Recurring
Variable Interest Entity [Line Items]
Investments	162,243	183,760
Derivatives	118	939
Total assets measured at fair value	293,036	311,100
Derivatives	1,834	871
Total liabilities measured at fair value	19,625	31,028
Level 2 | Recurring
Variable Interest Entity [Line Items]
Investments	17,565	8,952
Derivatives	21,623	12,552
Total assets measured at fair value	1,792,094	1,116,370
Derivatives	28,703	18,388
Total liabilities measured at fair value	28,703	18,388
Level 3 | Recurring
Variable Interest Entity [Line Items]
Investments	125	119
Derivatives	0	0
Total assets measured at fair value	125	119
Derivatives	0	0
Total liabilities measured at fair value	27,750	22,911
Consolidated company-sponsored investment funds | Recurring
Variable Interest Entity [Line Items]
Total assets measured at fair value	306,270	590,176
Total liabilities measured at fair value	7,557	9,642
Consolidated company-sponsored investment funds | Level 1 | Recurring
Variable Interest Entity [Line Items]
Total assets measured at fair value	74,351	132,554
Total liabilities measured at fair value	1,649	936
Consolidated company-sponsored investment funds | Level 2 | Recurring
Variable Interest Entity [Line Items]
Total assets measured at fair value	231,300	456,768
Total liabilities measured at fair value	5,908	8,706
Consolidated company-sponsored investment funds | Level 3 | Recurring
Variable Interest Entity [Line Items]
Total assets measured at fair value	619	854
Total liabilities measured at fair value	0	0
VIEs
Variable Interest Entity [Line Items]
Derivatives	3,224	4,833
Derivatives	6,893	4,559
VIEs | Recurring
Variable Interest Entity [Line Items]
Investments	242,541	404,624
Derivatives	3,224	4,833
Derivatives	6,893	4,559
VIEs | Level 1 | Recurring
Variable Interest Entity [Line Items]
Investments	73,909	28,270
Derivatives	442	139
Derivatives	1,649	835
VIEs | Level 2 | Recurring
Variable Interest Entity [Line Items]
Investments	168,114	375,559
Derivatives	2,782	4,694
Derivatives	5,244	3,724
VIEs | Level 3 | Recurring
Variable Interest Entity [Line Items]
Investments	518	795
Derivatives	0	0
Derivatives	0	0
VOEs
Variable Interest Entity [Line Items]
Derivatives	464	4,339
Derivatives	664	5,083
VOEs | Recurring
Variable Interest Entity [Line Items]
Investments	60,041	176,380
Derivatives	464	4,339
Derivatives	664	5,083
VOEs | Level 1 | Recurring
Variable Interest Entity [Line Items]
Investments	0	104,069
Derivatives	0	76
Derivatives	0	101
VOEs | Level 2 | Recurring
Variable Interest Entity [Line Items]
Investments	59,940	72,252
Derivatives	464	4,263
Derivatives	664	4,982
VOEs | Level 3 | Recurring
Variable Interest Entity [Line Items]
Investments	101	59
Derivatives	0	0
Derivatives	$ 0	$ 0