Fair Value Measurements for Operating Entities and Consolidated Funds - Unobservable Input Roll Forward (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Preferred Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		$ 59,967		$ 7,835		$ 5,168
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		45,530	[1]	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		1,653	[2]	1,000	[3]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		5,891		3,513
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		4,993		1,270
Realized and unrealized gains (losses), asset		7,357		1,424
Change in Unrealized Gain (Loss), instruments still held, asset	[4]	10,846		2,285
Common Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		23,936		17,466		9,850
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		102	[5]	10,242	[6],[7]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		29	[8],[9]	3	[10]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		7,288		11,477
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		3,818		11,002
Realized and unrealized gains (losses), asset		2,927		(3,098)
Change in Unrealized Gain (Loss), instruments still held, asset	[4]	1,990		(3,098)
Convertible Bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		6,040		2,500		3,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		0		4,826	[2],[3]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		3,787		11,354
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		1,050		7,072
Realized and unrealized gains (losses), asset		803		44
Change in Unrealized Gain (Loss), instruments still held, asset	[4]	803		(25)
Corporate Bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		135		2,421		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		0		4	[7]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		312	[2]	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		666		2,811
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		2,432		533
Realized and unrealized gains (losses), asset		(208)		139
Change in Unrealized Gain (Loss), instruments still held, asset	[4]	(180)		140
Options
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		251		336		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		0		330	[6]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		102	[5]	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		0		0
Realized and unrealized gains (losses), asset		17		6
Change in Unrealized Gain (Loss), instruments still held, asset	[4]	(1)		6
Warrants and Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		6,547		594		1,666
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		4,528	[1],[8]	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		0		189
Realized and unrealized gains (losses), asset		1,425		(883)
Change in Unrealized Gain (Loss), instruments still held, asset	[4]	1,425		31
Trade Claims
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		9,205		7,320		5,543
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		1,044	[8],[9]	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		4,774		7,205
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		2,944		5,506
Realized and unrealized gains (losses), asset		(989)		78
Change in Unrealized Gain (Loss), instruments still held, asset	[4]	(1,013)		76
Loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		12,623		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	[1]	11,149
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		245
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		0
Realized and unrealized gains (losses), asset		1,229
Change in Unrealized Gain (Loss), instruments still held, asset	[4]	1,229
Consolidated Funds | Preferred Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		0		4,393		24,314
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		4,000	[11]	19,929	[3]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		0		0
Realized and unrealized gains (losses), asset		(393)		8
Change in Unrealized Gain (Loss), instruments still held, asset	[4]	0		0
Consolidated Funds | Common Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		2,951		0		94
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		4,000	[11]	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		100,000	[12]	94	[3]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		100,000		407
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		0		958
Realized and unrealized gains (losses), asset		(1,049)		551
Change in Unrealized Gain (Loss), instruments still held, asset	[4]	(1,049)		0
Consolidated Funds | Convertible Bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		76,114
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		75,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		0
Realized and unrealized gains (losses), asset		1,114
Change in Unrealized Gain (Loss), instruments still held, asset	[4]	0
Consolidated Funds | Warrants and Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Asset Value		5,806		5,567		5,279
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales		0		1,758
Realized and unrealized gains (losses), asset		239		2,046
Change in Unrealized Gain (Loss), instruments still held, asset	[4]	239		289
Option
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value		3,915		2,920		2,096
Liability, Transfers In		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3		0		0
Liability, Purchases		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Sales		0		4
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings		(995)		(828)
Fair Value, Liability, Recurring Basis, Still Held, Unrealized Gain (Loss)	[4]	995		828
Contingent liability payable
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value		36,718		30,896		3,070
Liability, Transfers In		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3		1,235	[13]	0
Liability, Purchases		4,218	[14]	27,700
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Sales		5,653		1,234
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings		(8,492)		(1,360)
Fair Value, Liability, Recurring Basis, Still Held, Unrealized Gain (Loss)	[4]	8,492		1,360
Corporate Bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value		704		1,000		0
Liability, Transfers In		0		2,525	[7]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3		0		0
Liability, Purchases		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Sales		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings		(296)		(1,525)
Fair Value, Liability, Recurring Basis, Still Held, Unrealized Gain (Loss)	[4]	(248)		(1,525)
US Government Debt Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance Liability Value		1,500		1,950		$ 0
Liability, Transfers In		0		4,681	[7]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3		0		0
Liability, Purchases		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Sales		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings		(450)		(2,731)
Fair Value, Liability, Recurring Basis, Still Held, Unrealized Gain (Loss)	[4]	$ (450)		$ (2,731)

[1] The Company consolidated an operating entity which holds preferred stock, loans and warrants.

[2] The investments were converted to common stock.

[3] The entity in which the Company is invested completed an initial public offering

[4] Unrealized gains/losses are reported in other income (loss) in the accompanying consolidated statements of operations

[5] The options expired and converted into common stock.

[6] The holding Company which held common stock and options was liquidated.

[7] The investments had a change of valuation methodology due to increased activity in foreign market.

[8] The security stopped trading on an open market.

[9] The transfers between level 1 and level 3 are due to the change in the availability of observable inputs.

[10] Shares of common stock were exchanged for liquid warrants and rights of an acquired company.

[11] The investment was involved in a reverse merger and preferred stock was converted to common shares.

[12] The Company deconsolidated an investment fund.

[13] The contingent liability reached the end of its earnout period and is now valued based on actual cash payout.

[14] See Note 3 (MHT Acquisition) for contingent consideration recorded.