Consolidated Company-Sponsored Investment Funds (Fair Value) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives	$ 14,710	$ 17,079
Derivatives	16,658	14,822
Total liabilities measured at fair value	56,780	30,781
Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	149,142	216,251
Derivatives	1,282	1,594
Total assets measured at fair value	265,446	320,733
Derivatives	240	2,534
Total liabilities measured at fair value	13,930	11,157
Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	87,319	400,796
Derivatives	13,428	15,485
Total assets measured at fair value	1,058,896	1,585,835
Derivatives	16,418	12,288
Total liabilities measured at fair value	16,418	12,288
Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	118	142
Derivatives	0	0
Total assets measured at fair value	118	142
Derivatives	0	0
Total liabilities measured at fair value	26,432	7,336
Company-sponsored investment funds | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	549,093	358,922
Total liabilities measured at fair value	10,324	7,721
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	122,351	91,822
Total liabilities measured at fair value	578	269
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	420,341	258,727
Total liabilities measured at fair value	9,746	7,452
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	6,401	8,373
Total liabilities measured at fair value	0	0
VIEs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives	4,684	3,410
Derivatives	4,820	3,891
VIEs | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	372,668	217,840
Derivatives	4,684	3,410
Derivatives	4,820	3,891
VIEs | Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	27,424	22,149
Derivatives	164	1,486
Derivatives	521	72
VIEs | Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	339,350	187,626
Derivatives	4,520	1,924
Derivatives	4,299	3,819
VIEs | Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	5,894	8,065
Derivatives	0	0
Derivatives	0	0
VOEs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives	8,127	3,816
Derivatives	5,504	3,830
VOEs | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	163,614	133,856
Derivatives	8,127	3,816
Derivatives	5,504	3,830
VOEs | Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	94,725	68,063
Derivatives	38	124
Derivatives	57	197
VOEs | Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	68,382	65,485
Derivatives	8,089	3,692
Derivatives	5,447	3,633
VOEs | Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	507	308
Derivatives	0	0
Derivatives	$ 0	$ 0