Consolidated Company-Sponsored Investment Funds (Fair Value) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives	$ 10,054	$ 17,079
Derivatives	14,390	14,822
Total liabilities measured at fair value	27,123	30,781
Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	175,420	216,251
Derivatives	231	1,594
Total assets measured at fair value	268,937	320,733
Derivatives	1,672	2,534
Total liabilities measured at fair value	7,015	11,157
Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	6,248	400,796
Derivatives	9,823	15,485
Total assets measured at fair value	1,278,249	1,585,835
Derivatives	12,718	12,288
Total liabilities measured at fair value	12,718	12,288
Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	115	142
Derivatives	0	0
Total assets measured at fair value	115	142
Derivatives	0	0
Total liabilities measured at fair value	7,390	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	392,293	358,922
Total liabilities measured at fair value	6,718	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	112,105	91,822
Total liabilities measured at fair value	494	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	269,927	258,727
Total liabilities measured at fair value	6,224	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	10,261	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	2,624	3,410
Derivatives	2,780	3,891
VIEs | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	230,755	217,840
Derivatives	2,624	3,410
Derivatives	2,780	3,891
VIEs | Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	25,109	22,149
Derivatives	837	1,486
Derivatives	151	72
VIEs | Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	196,275	187,626
Derivatives	1,787	1,924
Derivatives	2,629	3,819
VIEs | Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	9,371	8,065
Derivatives	0	0
Derivatives	0	0
VOEs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives	4,360	3,816
Derivatives	3,938	3,830
VOEs | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	154,554	133,856
Derivatives	4,360	3,816
Derivatives	3,938	3,830
VOEs | Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	86,036	68,063
Derivatives	123	124
Derivatives	343	197
VOEs | Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	67,628	65,485
Derivatives	4,237	3,692
Derivatives	3,595	3,633
VOEs | Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	890	308
Derivatives	0	0
Derivatives	$ 0	$ 0