Fair Value Measurements for Operating Entities and Consolidated Funds - Fair Value Inputs, Unobservable Inputs, Quantitative Information (Details) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
		Mar. 31, 2021		Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Other investments		$ 366,783		$ 255,027
Contingent liability payable
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Liability Value		19,579		37,952	$ 28,658	$ 30,896
Options
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		241		251	332	336
Trade Claims
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		5,905		8,713	9,183	7,083
Warrants and Rights
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		7,924		6,547	598	594
Corporate Bonds
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		136		135	$ 2,812	$ 2,421
Level 3
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		118,315		127,461
Balance Liability Value		23,813		42,837
Level 3 | Derivative Liabilities | Valuation Technique, Option Pricing Model
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Liability Value		3,297
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	[1]	19,579
Level 3 | Contingent liability payable | Valuation Technique, Discounted Cash Flow
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Liability Value		$ 19,579		$ 36,718
Weighted average percent Fair Value technique		13.00%		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		7.00%		9.00%
Level 3 | Contingent liability payable | Valuation Technique, Discounted Cash Flow | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		15.00%		16.00%
Level 3 | Contingent liability payable | Monte Carlo [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Weighted average percent Fair Value technique		18.00%		22.00%
Level 3 | Contingent liability payable | Monte Carlo [Member] | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		18.00%		22.00%
Level 3 | Contingent liability payable | Monte Carlo [Member] | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		20.00%		24.00%
Level 3 | Other Liabilities [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Liability Value		$ 937	[2]	$ 2,204
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		$ 70,935		$ 65,735
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		12.00%		11.00%
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		11.00%		10.00%
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		20.00%		12.00%
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%		650.00%
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%		625.00%
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%		675.00%
Level 3 | Common and Preferred Stock | Valuation technique, probability of success
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		70.00%
Weighted average percent Fair Value technique		70.00%
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		$ 241		$ 251
Level 3 | Options | Valuation Technique, Discounted Cash Flow
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Weighted average percent Fair Value technique		12.00%		11.00%
Level 3 | Options | Valuation Technique, Discounted Cash Flow | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		11.00%		10.00%
Level 3 | Options | Valuation Technique, Discounted Cash Flow | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		12.00%		12.00%
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		$ 3,713		$ 3,500
Level 3 | Warrants and Rights | Market Approach, Income Approach and Replacement Cost Valuation Techniques [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value				$ 11,217
Level 3 | Warrants and Rights | Income Approach and Market Approach Valuation Techniques
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		$ 10,394
Level 3 | Warrants and Rights | Valuation Technique, Discounted Cash Flow
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Weighted average percent Fair Value technique		7.00%		7.00%
Level 3 | Warrants and Rights | Valuation Technique, Discounted Cash Flow | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		4.00%		4.00%
Level 3 | Warrants and Rights | Valuation Technique, Discounted Cash Flow | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		12.00%		11.00%
Level 3 | Warrants and Rights | Valuation, Market Approach
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Weighted average percent Fair Value technique		6.50%		6.50%
Level 3 | Warrants and Rights | Valuation, Market Approach | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		6.25%		6.25%
Level 3 | Warrants and Rights | Valuation, Market Approach | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		6.75%		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		$ 12,424		$ 12,623
Level 3 | Bonds | Valuation Technique, Discounted Cash Flow
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Weighted average percent Fair Value technique		12.00%		11.00%
Level 3 | Bonds | Valuation Technique, Discounted Cash Flow | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		11.00%		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%		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				650.00%
Level 3 | Bonds | Probability of recovery valuation technique | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs				625.00%
Level 3 | Bonds | Probability of recovery valuation technique | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs				675.00%
Level 3 | Other Investments
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value	[2]	$ 20,608		$ 34,135
Level 3 | Options | Valuation, Market Approach
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Weighted average percent Fair Value technique		650.00%		650.00%
Level 3 | Options | Valuation, Market Approach | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		625.00%		625.00%
Level 3 | Options | Valuation, Market Approach | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs		675.00%		675.00%
Fair Value, Measurements, Recurring | Level 3 | Option | Derivative Liabilities | 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				$ 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 inputs		20.00%		15.00%
Weighted average percent Fair Value technique		20.00%		15.00%
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%

[1] In accordance with the terms of the purchase agreements for acquisitions that closed during the first quarter of 2019 and the fourth quarter of 2020, 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, 2020 and December 31, 2023. For both the Quarton Acquisition and the MHT Acquisition, the Company estimated the contingent consideration liabilities using a combination of Monte Carlo and Discounted Cash Flow methods which require the Company to make estimates and assumptions regarding the future cash flows and profits. Changes in these estimates and assumptions could have a significant impact on the amounts recognized. The undiscounted amounts for the Quarton Acquisition can range from $10.1 million to $25.0 million. The undiscounted amounts for the MHT Acquisition have no minimum or maximum as it is calculated based on revenue.

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