Consolidated Company-Sponsored Investment Funds (Fair Value) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives	$ 32,566	$ 13,491
Derivatives	40,056	19,259
Total liabilities measured at fair value	91,389	72,327
Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	177,993	183,760
Derivatives	1,505	939
Total assets measured at fair value	303,265	311,100
Derivatives	4,895	871
Total liabilities measured at fair value	32,524	31,028
Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	17,589	8,952
Derivatives	31,061	12,552
Total assets measured at fair value	2,060,848	1,116,370
Derivatives	35,161	18,388
Total liabilities measured at fair value	35,161	18,388
Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	118	119
Derivatives	0	0
Total assets measured at fair value	118	119
Derivatives	0	0
Total liabilities measured at fair value	23,704	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	464,705	590,176
Total liabilities measured at fair value	19,316	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	99,108	132,554
Total liabilities measured at fair value	721	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	365,063	456,768
Total liabilities measured at fair value	18,595	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	534	854
Total liabilities measured at fair value	0	0
VIEs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives	7,892	4,833
Derivatives	6,603	4,559
VIEs | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	273,445	404,624
Derivatives	7,892	4,833
Derivatives	6,603	4,559
VIEs | Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	19,040	28,270
Derivatives	2,421	139
Derivatives	469	835
VIEs | Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	254,011	375,559
Derivatives	5,471	4,694
Derivatives	6,134	3,724
VIEs | Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	394	795
Derivatives	0	0
Derivatives	0	0
VOEs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives	13,341	4,339
Derivatives	12,713	5,083
VOEs | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	170,027	176,380
Derivatives	13,341	4,339
Derivatives	12,713	5,083
VOEs | Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	77,460	104,069
Derivatives	187	76
Derivatives	252	101
VOEs | Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	92,427	72,252
Derivatives	13,154	4,263
Derivatives	12,461	4,982
VOEs | Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	140	59
Derivatives	0	0
Derivatives	$ 0	$ 0