Consolidated Company-Sponsored Investment Funds (Fair Value) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives	$ 11,471	$ 17,079
Derivatives	21,329	14,822
Total liabilities measured at fair value	52,336	30,781
Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	133,672	216,251
Derivatives	220	1,594
Total assets measured at fair value	248,028	320,733
Derivatives	3,075	2,534
Total liabilities measured at fair value	8,479	11,157
Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	8,378	400,796
Derivatives	11,251	15,485
Total assets measured at fair value	1,129,218	1,585,835
Derivatives	18,254	12,288
Total liabilities measured at fair value	18,254	12,288
Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	117	142
Derivatives	0	0
Total assets measured at fair value	117	142
Derivatives	0	0
Total liabilities measured at fair value	25,603	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	475,581	358,922
Total liabilities measured at fair value	5,270	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	124,087	91,822
Total liabilities measured at fair value	662	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	339,660	258,727
Total liabilities measured at fair value	4,608	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	11,834	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	4,029	3,410
Derivatives	4,003	3,891
VIEs | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	304,067	217,840
Derivatives	4,029	3,410
Derivatives	4,003	3,891
VIEs | Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	27,049	22,149
Derivatives	1,454	1,486
Derivatives	317	72
VIEs | Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	266,235	187,626
Derivatives	2,575	1,924
Derivatives	3,686	3,819
VIEs | Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	10,783	8,065
Derivatives	0	0
Derivatives	0	0
VOEs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives	1,117	3,816
Derivatives	1,267	3,830
VOEs | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	166,368	133,856
Derivatives	1,117	3,816
Derivatives	1,267	3,830
VOEs | Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	95,439	68,063
Derivatives	145	124
Derivatives	345	197
VOEs | Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	69,878	65,485
Derivatives	972	3,692
Derivatives	922	3,633
VOEs | Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	1,051	308
Derivatives	0	0
Derivatives	$ 0	$ 0