Fair Value Measurements for Operating Entities and Consolidated Funds - Fair Value Inputs, Unobservable Inputs, Quantitative Information (Details) $ in Thousands		Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Dec. 31, 2020 USD ($) times	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Other investments		$ 262,431		$ 255,027
Contingent liability payable
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Liability Value		29,053	$ 24,810	37,952	$ 30,024	$ 27,001	$ 30,896
Options (held long)
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		238	244	251	351	337	336
Trade Claims
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		5,681	5,719	8,713	9,005	7,155	7,083
Warrants and Rights
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		13,056	11,631	6,548	4,983	4,625	594
Corporate Bonds
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		83	$ 107	135	$ 520	$ 758	$ 2,421
Level 3
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		186,958		127,461
Balance Liability Value		$ 32,387		$ 42,837
Level 3 | Contingent liability payable | Valuation Technique, Discounted Cash Flow | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		0.07		0.09
Level 3 | Contingent liability payable | Valuation Technique, Discounted Cash Flow | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		0.15		0.16
Level 3 | Contingent liability payable | Valuation Technique, Discounted Cash Flow | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		0.13		0.15
Level 3 | Contingent liability payable | Discount Cash Flow and Monte Carlo Technique
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Liability Value		$ 29,053		$ 36,718
Level 3 | Contingent liability payable | Volatility | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		0.19		0.22
Level 3 | Contingent liability payable | Volatility | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		0.20		0.24
Level 3 | Contingent liability payable | Volatility | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		0.20		0.22
Level 3 | Other Liabilities [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Liability Value	[1]			$ 2,204
Level 3 | Common and Preferred Stock | Discounted Cash Flow and Market Approach Valuation Techniques
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		$ 64,414		$ 65,735
Level 3 | Common and Preferred Stock | Valuation Technique, Discounted Cash Flow | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		0.12		0.10
Level 3 | Common and Preferred Stock | Valuation Technique, Discounted Cash Flow | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		0.20		0.12
Level 3 | Common and Preferred Stock | Valuation Technique, Discounted Cash Flow | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		0.125		0.11
Level 3 | Common and Preferred Stock | Valuation, Market Approach | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		6.25		6.25
Level 3 | Common and Preferred Stock | Valuation, Market Approach | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		6.75		6.75
Level 3 | Common and Preferred Stock | Valuation, Market Approach | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		6.5		6.5
Level 3 | Options (held long) | Discounted Cash Flow and Market Approach Valuation Techniques
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		$ 238		$ 251
Level 3 | Options (held long) | Valuation Technique, Discounted Cash Flow | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		0.10		0.10
Level 3 | Options (held long) | Valuation Technique, Discounted Cash Flow | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		0.13		0.12
Level 3 | Options (held long) | Valuation Technique, Discounted Cash Flow | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		0.125		0.11
Level 3 | Trade Claims | Valuation Technique, Discounted Cash Flow
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		$ 2,639		$ 3,500
Level 3 | Warrants and Rights | Discounted Cash Flow and Market Approach Valuation Techniques
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		$ 4,512		$ 11,217
Level 3 | Warrants and Rights | Valuation Technique, Discounted Cash Flow | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		0.12		0.04
Level 3 | Warrants and Rights | Valuation Technique, Discounted Cash Flow | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		0.13		0.11
Level 3 | Warrants and Rights | Valuation Technique, Discounted Cash Flow | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		0.125		0.07
Level 3 | Warrants and Rights | Valuation, Market Approach | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		0.0625		0.0625
Level 3 | Warrants and Rights | Valuation, Market Approach | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		0.0675		0.0675
Level 3 | Warrants and Rights | Valuation, Market Approach | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		0.065		0.065
Level 3 | Corporate Bonds | Discounted Cash Flow and Market Approach Valuation Techniques
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		$ 12,578		$ 12,623
Level 3 | Corporate Bonds | Valuation Technique, Discounted Cash Flow | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		0.12		0.10
Level 3 | Corporate Bonds | Valuation Technique, Discounted Cash Flow | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		0.13		0.12
Level 3 | Corporate Bonds | Valuation Technique, Discounted Cash Flow | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		0.125		0.11
Level 3 | Corporate Bonds | Valuation, Market Approach | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		6.25		6.25
Level 3 | Corporate Bonds | Valuation, Market Approach | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		6.75		6.75
Level 3 | Corporate Bonds | Valuation, Market Approach | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		6.5		6.5
Level 3 | Other Investments
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value	[1]	$ 102,577		$ 34,135
Level 3 | Options (held long) | Valuation, Market Approach | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		6.25		6.25
Level 3 | Options (held long) | Valuation, Market Approach | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		6.75		6.75
Level 3 | Options (held long) | Valuation, Market Approach | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		6.5		6.5
Fair Value, Measurements, Recurring | Level 3 | Options (held short) | Derivative Liabilities | Valuation Technique, Option Pricing Model
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Liability Value		$ 3,334		$ 3,915
Discount rate | Level 3 | Trade Claims | Valuation Technique, Discounted Cash Flow
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		0.20		0.15
Discount rate | Level 3 | Trade Claims | Valuation Technique, Discounted Cash Flow | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		0.20		0.15
Volatility | Level 3 | Options (held short) | Valuation Technique, Option Pricing Model
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		0.35		0.35
Volatility | Level 3 | Options (held short) | Valuation Technique, Option Pricing Model | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Measurement Input		0.35		0.35

[1] The quantitative disclosures exclude financial instruments for which the determination of fair value is based on prices from recent transactions.