Consolidation - Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Noncontrolling interests	$ (60,502)	$ (59,003)	$ (57,481)	$ (3,420)	$ (4,162)	$ (4,178)
VOEs
Variable Interest Entity [Line Items]
Cash and cash equivalents	776		1,029
Investments	21,731		12,923
Other assets	3,997		228
Notes payable	0		0
Securities purchased payable and other liabilities	(4,378)		(823)
Noncontrolling interests	(5,926)		(2,348)
The Company’s net interests in consolidated investment products	16,200		11,009
CLOs
Variable Interest Entity [Line Items]
Cash and cash equivalents	84,318		51,363
Investments	1,910,875		1,709,266
Other assets	9,261		30,426
Notes payable	(1,831,129)		(1,620,260)
Securities purchased payable and other liabilities	(75,554)		(69,737)
Noncontrolling interests	(12,637)		(13,958)
The Company’s net interests in consolidated investment products	85,134		87,100
Other
Variable Interest Entity [Line Items]
Cash and cash equivalents	164		559
Investments	30,870		27,379
Other assets	700		403
Notes payable	0		0
Securities purchased payable and other liabilities	(511)		(146)
Noncontrolling interests	(920)		(36)
The Company’s net interests in consolidated investment products	$ 30,303		$ 28,159