Fair Value Measurements - Classes of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financial Assets
Investments—Consolidated Investment Companies	$ 55,007	$ 64,526
Investments—Affiliates and Other	39,756	26,935
Fair Value, Measurements, Recurring
Financial Assets
Cash and Cash Equivalents	277,840	249,174
Investments—Consolidated Investment Companies	55,007	64,526
Investments—Affiliates and Other	39,756	26,935
Other	8,591	6,078
Total Financial Assets	381,194	346,713
Financial Liabilities
Total Financial Liabilities	11,091	2,087
Fair Value, Measurements, Recurring | Level 1
Financial Assets
Cash and Cash Equivalents	277,840	249,174
Investments—Consolidated Investment Companies	9,197	7,245
Investments—Affiliates and Other	34,062	23,667
Other	8,537	2,901
Total Financial Assets	329,636	282,987
Financial Liabilities
Total Financial Liabilities	45	6
Fair Value, Measurements, Recurring | Level 2
Financial Assets
Cash and Cash Equivalents	0	0
Investments—Consolidated Investment Companies	45,810	57,281
Investments—Affiliates and Other	5,364	2,945
Other	54	3,177
Total Financial Assets	51,228	63,403
Financial Liabilities
Total Financial Liabilities	1,261	0
Fair Value, Measurements, Recurring | Level 3
Financial Assets
Cash and Cash Equivalents	0	0
Investments—Consolidated Investment Companies	0	0
Investments—Affiliates and Other	330	323
Other	0	0
Total Financial Assets	330	323
Financial Liabilities
Total Financial Liabilities	$ 9,785	$ 2,081