Consolidation - Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Noncontrolling interests	$ (99,277)	$ (90,687)	$ (63,845)	$ (91,610)	$ (60,502)	$ (57,481)
VOEs
Variable Interest Entity [Line Items]
Cash and cash equivalents	9,128		2,665
Investments	46,623		22,223
Other assets	2,756		1,563
Notes payable	0		0
Securities purchased payable and other liabilities	(2,972)		(2,964)
Noncontrolling interests	(22,362)		(3,865)
Net interests in CIP	33,173		19,622
CLOs
Variable Interest Entity [Line Items]
Cash and cash equivalents	43,930		97,130
Investments	2,231,691		1,976,148
Other assets	23,821		21,450
Notes payable	(2,190,937)		(1,834,535)
Securities purchased payable and other liabilities	(37,378)		(164,887)
Noncontrolling interests	(8,982)		(10,558)
Net interests in CIP	62,145		84,748
Other
Variable Interest Entity [Line Items]
Cash and cash equivalents	1,177		363
Investments	55,371		31,739
Other assets	838		599
Notes payable	0		0
Securities purchased payable and other liabilities	(670)		(200)
Noncontrolling interests	(2,289)		(1,564)
Net interests in CIP	$ 54,427		$ 30,937