Consolidated Company-Sponsored Investment Funds (Fair Value) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives	$ 7,768	$ 8,413
Total assets measured at fair value	1,606,162	1,291,395
Short equities	14,921	40,252
Derivatives	10,347	8,649
Total liabilities measured at fair value	43,361	67,182
Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives	536	1,224
Total assets measured at fair value	365,906	340,226
Short equities	14,921	40,252
Derivatives	1,909	1,092
Total liabilities measured at fair value	17,746	42,036
Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives	7,232	7,189
Total assets measured at fair value	1,235,230	946,146
Short equities	0	0
Derivatives	8,438	7,557
Total liabilities measured at fair value	8,438	7,557
Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives	0	0
Total assets measured at fair value	5,026	5,023
Short equities	0	0
Derivatives	0	0
Total liabilities measured at fair value	17,177	17,589
Consolidated Investment Portfolios [Member] | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	757,900	574,814
Total liabilities measured at fair value	386,500	250,500
Consolidated Investment Portfolios [Member] | Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	506,016	352,076
Total liabilities measured at fair value	381,652	248,467
Consolidated Investment Portfolios [Member] | Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	241,611	216,997
Total liabilities measured at fair value	4,848	2,033
Consolidated Investment Portfolios [Member] | Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	10,273	5,741
Total liabilities measured at fair value	0	0
VIEs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives	25,255	4,997
Derivatives	4,868	2,081
VIEs | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	730,453	550,768
Derivatives	4,358	1,797
Derivatives	4,868	2,081
VIEs | Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	494,620	341,830
Derivatives	39	58
Derivatives	20	48
VIEs | Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	225,560	203,197
Derivatives	4,319	1,739
Derivatives	4,848	2,033
VIEs | Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	10,273	5,741
Derivatives	0	0
Derivatives	0	0
VIEs | Short | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short equities	381,632	248,419
VIEs | Short | Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short equities	381,632	248,419
VIEs | Short | Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short equities	0	0
VIEs | Short | Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short equities	0	0
VOEs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives	43
Derivatives	0
VOEs | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	23,076	22,249
Derivatives	13
Derivatives	0
VOEs | Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	11,357	10,188
Derivatives	0
Derivatives	0
VOEs | Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	11,719	12,061
Derivatives	13
Derivatives	0
VOEs | Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	$ 0
Derivatives	0
Derivatives	$ 0