Fair Value Measurements for Operating Entities and Consolidated Funds - Fair Value Inputs, Unobservable Inputs, Quantitative Information (Details) - USD ($) $ in Thousands		9 Months Ended		12 Months Ended
		Sep. 30, 2020		Dec. 31, 2019	Jun. 30, 2020	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Contingent liability payable
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Liability Value		$ 30,024		$ 30,896	$ 27,001	$ 29,834	$ 29,536	$ 3,070
Options
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		351		336	337
Trade Claims
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		9,390		7,320	7,587	7,062	10,488	5,543
Warrants and Rights [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		4,983		594	4,625	584	595	1,666
Corporate Bonds
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		520		2,421	758	$ 2,073	$ 775	$ 0
Balance Liability Value		800			$ 800
Level 3
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		289,703		48,432
Balance Liability Value		35,278		36,766
Level 3 | Contingent liability payable | Market Approach, Income Approach and Replacement Cost Valuation Techniques [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Liability Value		$ 30,024	[1]	$ 30,896
Level 3 | Contingent liability payable | Valuation Technique, Discounted Cash Flow
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Weighted average percent Fair Value technique		15.00%		15.00%
Level 3 | Contingent liability payable | Valuation Technique, Discounted Cash Flow | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		15.00%		15.00%
Level 3 | Contingent liability payable | Valuation Technique, Discounted Cash Flow | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		22.00%		22.00%
Level 3 | Contingent liability payable | Monte Carlo [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		22.00%		17.00%
Weighted average percent Fair Value technique		22.00%		17.00%
Level 3 | Other Liabilities [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Liability Value		$ 2,300	[2]	$ 2,950
Level 3 | Common and Preferred Stock | Market Approach, Income Approach and Replacement Cost Valuation Techniques [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		$ 61,220		$ 10,876
Level 3 | Common and Preferred Stock | Valuation Technique, Discounted Cash Flow
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Weighted average percent Fair Value technique		11.00%		10.40%
Level 3 | Common and Preferred Stock | Valuation Technique, Discounted Cash Flow | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		10.00%		8.00%
Level 3 | Common and Preferred Stock | Valuation Technique, Discounted Cash Flow | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		12.00%		11.25%
Level 3 | Common and Preferred Stock | Valuation, Market Approach
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Weighted average percent Fair Value technique		650.00%		675.00%
Level 3 | Common and Preferred Stock | Valuation, Market Approach | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		625.00%		650.00%
Level 3 | Common and Preferred Stock | Valuation, Market Approach | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		675.00%		700.00%
Level 3 | Options | Market Approach, Income Approach and Replacement Cost Valuation Techniques [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		$ 352		$ 336
Level 3 | Options | Valuation Technique, Discounted Cash Flow
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Weighted average percent Fair Value technique		11.00%		10.50%
Level 3 | Options | Valuation Technique, Discounted Cash Flow | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		10.00%		9.75%
Level 3 | Options | Valuation Technique, Discounted Cash Flow | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		12.00%		11.25%
Level 3 | Trade Claims | Market Approach, Income Approach and Replacement Cost Valuation Techniques [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		$ 3,446		$ 24
Level 3 | Warrants and Rights [Member] | Market Approach, Income Approach and Replacement Cost Valuation Techniques [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value				$ 6,162
Level 3 | Warrants and Rights [Member] | Income Approach and Market Approach Valuation Techniques
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		$ 10,865
Level 3 | Warrants and Rights [Member] | Valuation Technique, Discounted Cash Flow
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Weighted average percent Fair Value technique		7.00%		6.10%
Level 3 | Warrants and Rights [Member] | Valuation Technique, Discounted Cash Flow | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		4.00%		6.00%
Level 3 | Warrants and Rights [Member] | Valuation Technique, Discounted Cash Flow | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		11.00%		7.00%
Level 3 | Warrants and Rights [Member] | Valuation, Market Approach
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Weighted average percent Fair Value technique		6.50%
Level 3 | Warrants and Rights [Member] | Valuation, Market Approach | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		6.25%
Level 3 | Warrants and Rights [Member] | Valuation, Market Approach | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		6.75%
Level 3 | Corporate Bonds | Income Approach and Market Approach Valuation Techniques
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		$ 12,110		$ 311
Level 3 | Bonds | Valuation Technique, Discounted Cash Flow
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs				20.00%
Weighted average percent Fair Value technique		11.00%		20.00%
Level 3 | Bonds | Valuation Technique, Discounted Cash Flow | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		10.00%
Level 3 | Bonds | Valuation Technique, Discounted Cash Flow | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		12.00%
Level 3 | Bonds | Valuation, Market Approach
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Weighted average percent Fair Value technique		650.00%
Level 3 | Bonds | Valuation, Market Approach | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		625.00%
Level 3 | Bonds | Valuation, Market Approach | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		675.00%
Level 3 | Bonds | Probability of recovery valuation technique
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Weighted average percent Fair Value technique				2.30%
Level 3 | Bonds | Probability of recovery valuation technique | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs				1.00%
Level 3 | Bonds | Probability of recovery valuation technique | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs				3.00%
Level 3 | Other Investments
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value	[2]	$ 201,710		$ 30,723
Level 3 | Options | Valuation, Market Approach
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Weighted average percent Fair Value technique		650.00%		675.00%
Level 3 | Options | Valuation, Market Approach | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		625.00%		650.00%
Level 3 | Options | Valuation, Market Approach | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		675.00%		700.00%
Fair Value, Measurements, Recurring | Level 3 | Option | Options | Market Approach, Income Approach and Replacement Cost Valuation Techniques [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Financial Liabilities Fair Value Disclosure		$ 2,954		$ 2,920
Discount rate | Level 3 | Trade Claims | Valuation Technique, Discounted Cash Flow
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		15.00%		20.00%
Weighted average percent Fair Value technique		15.00%		20.00%
Volatility | Level 3 | Warrants and Rights [Member] | Market Approach Valuation Technique
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs				30.00%
Weighted average percent Fair Value technique				0.00%
Volatility | Level 3 | Option | Market Approach Valuation Technique
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		35.00%
Weighted average percent Fair Value technique		35.00%		35.00%
Volatility | Level 3 | Option | Market Approach Valuation Technique | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs				35.00%
Volatility | Level 3 | Option | Market Approach Valuation Technique | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs				40.00%

[1] In accordance with the terms of the purchase agreements for acquisitions that closed during the second quarter of 2016 and the first quarter of 2019, the Company is required to pay to the sellers a portion of future net income and/or revenues of the acquired businesses, if certain targets are achieved through the periods ended December 31, 2019 and December 31, 2023, respectively. For the acquisition that closed during 2016, the Company estimated the contingent consideration liability using the income approach (discounted cash flow method) which requires the Company to make estimates and assumptions regarding the future cash flows and profits. For the acquisition that closed during 2019, the Company estimated the contingent consideration liability using the present value of the Monte Carlo simulated revenue. Changes in these estimates and assumptions could have a significant impact on the amounts recognized. The undiscounted amounts as of September 30, 2020 can range from $0.9 million to $35.1 million.

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