Consolidation - Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Noncontrolling interests	$ (60,248)	$ (4,178)	$ (67,227)	$ (37,266)
VOEs
Variable Interest Entity [Line Items]
Cash and cash equivalents	911	820
Investments	30,137	34,623
Other assets	162	767
Notes payable	0	0
Securities purchased payable and other liabilities	(989)	(1,319)
Noncontrolling interests	(3,961)	(4,178)
The Company’s net interests in consolidated investment vehicles	26,260	30,713
CLOs
Variable Interest Entity [Line Items]
Cash and cash equivalents	49,868	82,823
Investments	1,737,518	1,555,879
Other assets	16,346	32,671
Notes payable	(1,608,735)	(1,457,435)
Securities purchased payable and other liabilities	(82,709)	(110,871)
Noncontrolling interests	(15,507)	(16,667)
The Company’s net interests in consolidated investment vehicles	96,781	86,400
Other
Variable Interest Entity [Line Items]
Cash and cash equivalents	415	18,489
Investments	23,724	7,250
Other assets	380	48
Notes payable	0	0
Securities purchased payable and other liabilities	(366)	(764)
Noncontrolling interests	0	0
The Company’s net interests in consolidated investment vehicles	$ 24,153	$ 25,023