Investments of Operating Entities and Consolidated Funds - Indirect Concentration of the Underlying Investments Held by Consolidated Funds (Details) $ in Thousands	Sep. 30, 2019 USD ($) investments	Dec. 31, 2018 USD ($) investments
Investment [Line Items]
Concentration of risk, number of investments \| investments	1	1
Equity Securities \| Linkem \| ITALY \| 517210 Wireless Telecommunications Carriers (except Satellite)
Investment [Line Items]
Market Value	$ 69,927
Equity Securities \| Linkem \| ITALY \| 517312 Wireless Telecommunications Carriers (except Satellite) [Member]
Investment [Line Items]
Percentage of Stockholders' Equity	8.55842%	8.36%
Market Value		$ 66,439

Value of the investment at close of period. For schedules of investments that are categorized, the value would be aggregated by category. For investment in and advances to affiliates, if operations of any controlled companies are different in character from those of the company, group such affiliates within divisions and by type of activities.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
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-Section 50
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
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Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant