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, 2015		Dec. 31, 2014		Jun. 30, 2015	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2013
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		$ 63,053		$ 55,006
Financial Liabilities Fair Value Disclosure		282,275		253,288
Assets, Fair Value Disclosure, Recurring		927,523		845,131
Balance Liability Value		27,049		40,890
Contingent liability payable
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Financial Liabilities Fair Value Disclosure		5,458	[1]	4,083	[2]
Balance Liability Value		5,458		4,083		$ 2,358	$ 6,419	$ 6,783	$ 6,937
Common and Preferred Stock
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		3,110		12,269
Convertible Bonds
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		1,129		900		879	1,750	1,750	1,950
Assets, Fair Value Disclosure, Recurring		1,129		900
Warrants and Rights
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value		2,994		1,322		$ 2,316	$ 2,608	$ 3,346	$ 5,805
Assets, Fair Value Disclosure, Recurring		3,871		1,417
Other Investments
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Balance Asset Value	[3]	34,229		3,708
Level 3
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Financial Liabilities Fair Value Disclosure		27,049		40,890
Assets, Fair Value Disclosure, Recurring		$ 63,053		$ 55,006
Level 3 | Options | Market Approach Valuation Technique
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Volatility		29.00%
Level 3 | Options | Market Approach Valuation Technique | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Volatility				30.00%
Fair Value Assumptions, Credit Spread				5.00%
Level 3 | Options | Market Approach Valuation Technique | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Volatility				40.00%
Fair Value Assumptions, Credit Spread				7.50%
Level 3 | Contingent liability payable
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Financial Liabilities Fair Value Disclosure		$ 5,458	[1]	$ 4,083	[2]
Level 3 | Contingent liability payable | Income Approach and Market Approach Valuation Techniques
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
DCF discount rate				9.00%
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		9.00%
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		24.50%
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		18.00%
Level 3 | Common and Preferred Stock | Market Approach Valuation Technique
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Volatility		42.00%		45.00%
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		1		1
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		5.25		6
Level 3 | Convertible Bonds
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Assets, Fair Value Disclosure, Recurring		$ 1,129		$ 900
Level 3 | Convertible Bonds | Cost Approach Valuation Technique [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs, Recovery Rate		50.00%		50.00%
Level 3 | Warrants and Rights
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Assets, Fair Value Disclosure, Recurring		$ 2,994		$ 1,322
Level 3 | Warrants and Rights | Market Approach Valuation Technique
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Assumptions, Weighted Average Volatility Rate		29.00%		34.00%
Level 3 | Warrants and Rights | Market Approach Valuation Technique | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Volatility		17.00%		20.00%
Level 3 | Warrants and Rights | Market Approach Valuation Technique | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Volatility		60.00%		60.00%
Level 3 | Options | Market Approach Valuation Technique
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Volatility		29.00%
Level 3 | Options | Market Approach Valuation Technique | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Volatility				30.00%
Fair Value Assumptions, Credit Spread				5.00%
Level 3 | Options | Market Approach Valuation Technique | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Volatility				40.00%
Fair Value Assumptions, Credit Spread				7.50%
Options | Derivative Assets
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Assets, Fair Value Disclosure, Recurring		$ 40,944		$ 49,241
Options | Level 3 | Derivative Assets
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Assets, Fair Value Disclosure, Recurring		$ 21,591		$ 36,807

[1] In accordance with the terms of the purchase agreements for acquisitions that closed during 2012 and the third quarter of 2015, the Company is required to pay to the sellers a portion of future net income of the acquired businesses, if certain revenue targets are achieved through the periods ended August 2016 and December 2020, 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 September 30, 2015 can range from zero to $6.7 million.

[2] In accordance with the terms of a purchase agreement for an acquisitions that closed during 2012, the Company is required to pay to the sellers a portion of future net income of the acquired businesses, if certain revenue targets are achieved through the period ended August 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. Changes in these estimates and assumptions could have a significant impact on the amounts recognized. The undiscounted amounts can range from $0.9 million to $7.1 million.

[3] The quantitative disclosures exclude financial instruments for which the determination of fair value is based on prices from prior transactions and investments for which NAV per share is used as a practical expedient to determine fair value.