Segment Reporting (Details) $ in Thousands		12 Months Ended
		Dec. 31, 2020 USD ($) segment	Dec. 31, 2019 USD ($)		Dec. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment		2
Reconciliation to U.S. GAAP Company's Economic Income (Loss)
Preferred stock dividends		$ 6,792	$ 6,792		$ 6,792
Amortization of (discount)/premium on convertible debt		4,490	4,598		5,473
Goodwill and other impairment		22,677	20,460		12,436
Income (loss) before income taxes		297,437	70,723		95,598
Segment Information
Total revenues		1,623,304	1,049,443		966,916
Depreciation and Amortization		22,677	20,460		12,436
Interest and Dividend Expense		187,725	168,628		104,116
Dividend expense		8,100	8,800		6,600
Dividend revenue		17,300	9,200		10,200
Consolidated Funds
Segment Information
Interest and Dividend Expense		2,064	4,602		6,534
Dividend expense		700	1,000		1,900
Dividend revenue		2,500	3,000		5,400
Operating Segments
Segment Information
Non-Interest Revenue	[1]	1,450,484	876,961		864,732
Interest Revenue		170,128	165,727		97,759
Total revenues		1,623,304	1,049,443		966,916
Operating Segments | Consolidated Funds
Segment Information
Interest Revenue		2,692	6,755		4,425
Adjustments
Reconciliation to U.S. GAAP Company's Economic Income (Loss)
Noncontrolling Interest		(9,299)	31,239		37,060
Preferred stock dividends		6,792	6,792		6,792
Amortization of (discount)/premium on convertible debt		(4,499)	(4,297)		(4,010)
Transaction-related and other costs		(9,098)	(2,608)		(2,778)
Goodwill and other impairment		(2,423)	(4,100)		0
Unrealized gain (loss) on conversion option		0	0	[2]	(7,416)	[2]
Debt extinguishment gain / loss		2,719	0		(556)
Exited business cost		0	0		(2,395)
OpCo | Operating Segments
Reconciliation to U.S. GAAP Company's Economic Income (Loss)
Economic Income		329,381	53,257		77,935
Segment Information
Non-Interest Revenue		1,447,595	874,506		856,285
Interest Revenue		169,358	165,443		96,535
Total revenues		1,619,636	1,046,695		957,233
Interest Expense		173,537	155,974		94,555
Depreciation and Amortization		22,655	20,424		11,402
OpCo | Operating Segments | Consolidated Funds
Segment Information
Interest Revenue		2,683	6,746		4,413
Interest Expense		1,376	3,553		4,606
Asset Co | Operating Segments
Reconciliation to U.S. GAAP Company's Economic Income (Loss)
Economic Income		(16,136)	(9,560)		(9,034)
Segment Information
Non-Interest Revenue		2,889	2,455		8,447
Interest Revenue		770	284		1,224
Total revenues		3,668	2,748		9,683
Interest Expense		6,120	3,835		2,920
Depreciation and Amortization		22	36		1,034
Asset Co | Operating Segments | Consolidated Funds
Segment Information
Interest Revenue		9	9		12
Interest Expense		$ 0	$ 0		$ 0

[1] Includes dividend revenue of $17.3 million, $9.2 million and $10.2 million for the years ended December 31, 2020, 2019, and 2018, respectively. In addition, includes dividend revenue, consolidated funds, of $2.5 million, $3.0 million and $5.4 million for the years ended December 31, 2020, 2019, and 2018, respectively.

[2] Prior to the Company's June 26, 2018 stockholder meeting, the embedded conversion option feature associated with its December 2022 Convertible Notes was recognized at fair value in accordance with US GAAP as a derivative liability. The profit and loss movement related to that liability was associated with the movement of the per share price of the Company's Class A common stock. Subsequent to receiving stockholder approval for share settlement the embedded conversion option was reclassified to equity and will no longer result in profit and loss movements.