Fair Value Measurements for Operating Entities and Consolidated Funds Fair Value Inputs, Unobservable Inputs, Quantitative Information (Details) $ in Thousands		3 Months Ended
		Mar. 31, 2018 USD ($)		Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)		Dec. 31, 2016 USD ($)
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Financial Liabilities Fair Value Disclosure		$ 315,881			$ 395,847
Contingent liability payable
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Financial Liabilities Fair Value Disclosure		3,440	[1]		3,440
Balance Liability Value		3,440		$ 5,274	3,440		$ 5,997
Trade Claims
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		5,955		703	5,950		562
Warrants and Rights
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		1,702		4,139	2,517		3,719
Options
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		0		$ 6,971	1,455		$ 14,753
Put Option | Options
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Financial Liabilities Fair Value Disclosure		47,423			41,563
Level 3
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		41,383			80,253
Financial Liabilities Fair Value Disclosure		24,835			25,841
Balance Liability Value		$ 24,835			25,841
Level 3 | Options | Market Approach Valuation Technique
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Volatility				28.00%
Level 3 | Options | Market Approach Valuation Technique | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Volatility		30.00%
Level 3 | Options | Market Approach Valuation Technique | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Volatility		37.00%
Level 3 | Contingent liability payable
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Financial Liabilities Fair Value Disclosure		$ 3,440	[1]		3,440	[2]
Level 3 | Contingent liability payable | Income Approach and Market Approach Valuation Techniques | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
DCF discount rate		8.00%		8.00%
Level 3 | Contingent liability payable | Income Approach and Market Approach Valuation Techniques | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
DCF discount rate		23.00%		23.00%
Level 3 | Contingent liability payable | Market Approach Valuation Technique
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Assumptions, Weighted Average Volatility Rate		22.00%		22.00%
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					3,440
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		$ 3,411			5,642
DCF discount rate		50.00%
Level 3 | Common and Preferred Stock | Market Approach, Income Approach and Replacement Cost Valuation Techniques [Member] | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Market multiple		4.5		4.8
Level 3 | Common and Preferred Stock | Market Approach, Income Approach and Replacement Cost Valuation Techniques [Member] | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Market multiple		8.5		8.5
Level 3 | Trade Claims | Market Approach Valuation Technique
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
DCF discount rate		20.00%		20.00%
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		$ 72			70
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		$ 1,702
Level 3 | Warrants and Rights | Market Approach Valuation Technique | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
DCF discount rate		8.00%
Volatility				61.00%
Level 3 | Warrants and Rights | Market Approach Valuation Technique | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
DCF discount rate		9.00%
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					2,516
Level 3 | Other Investments | Income Approach and Market Approach Valuation Techniques
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value	[3]	$ 36,198
Level 3 | Other Investments | Market Approach, Income Approach and Replacement Cost Valuation Techniques [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value	[3]				70,570
Level 3 | Options | Market Approach Valuation Technique
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Volatility				28.00%
Level 3 | Options | Derivative Assets | Market Approach, Income Approach and Replacement Cost Valuation Techniques [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value					1,455
Level 3 | Put Option | Options
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Financial Liabilities Fair Value Disclosure		$ 21,395			22,401
Level 3 | Put 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					$ 22,401

[1] In accordance with the terms of the purchase agreements for acquisitions that closed during the third and fourth quarter of 2015 and the second quarter of 2016, 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 2018, December 2020, and June 2018, respectively. 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. Changes in these estimates and assumptions could have a significant impact on the amounts recognized. The undiscounted amounts as of March 31, 2018 can range from $0.1 million to $15.0 million.

[2] In accordance with the terms of the purchase agreements for acquisitions that closed during the third and fourth quarter of 2015 and the second quarter of 2016, 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 2018, December 2020, and June 2018, respectively. 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. Changes in these estimates and assumptions could have a significant impact on the amounts recognized. The undiscounted amounts as of December 31, 2017 can range from $0.1 million to $15.0 million.

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