Consolidation - Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Noncontrolling interests	$ (91,610)	$ (60,502)	$ (57,481)	$ (60,248)	$ (3,420)	$ (4,178)
VOEs
Variable Interest Entity [Line Items]
Cash and cash equivalents	8,717		1,029
Investments	79,434		12,923
Other assets	2,584		228
Notes payable	0		0
Securities purchased payable and other liabilities	(2,658)		(823)
Noncontrolling interests	(37,307)		(2,348)
Net interests in CIP	50,770		11,009
CLOs
Variable Interest Entity [Line Items]
Cash and cash equivalents	74,032		51,363
Investments	1,908,324		1,709,266
Other assets	13,684		30,426
Notes payable	(1,821,243)		(1,620,260)
Securities purchased payable and other liabilities	(81,018)		(69,737)
Noncontrolling interests	(11,912)		(13,958)
Net interests in CIP	81,867		87,100
Other
Variable Interest Entity [Line Items]
Cash and cash equivalents	413		559
Investments	31,165		27,379
Other assets	554		403
Notes payable	0		0
Securities purchased payable and other liabilities	(377)		(146)
Noncontrolling interests	(1,167)		(36)
Net interests in CIP	$ 30,588		$ 28,159