Consolidation - Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Cash and cash equivalents	$ 180,528	$ 234,282	$ 179,893	$ 83,671
Noncontrolling interests	(3,420)	(4,178)	$ (57,336)	$ (37,266)
VOEs
Variable Interest Entity [Line Items]
Cash and cash equivalents	910	820
Investments	28,756	34,623
Other assets	257	767
Notes payable	0	0
Securities purchased payable and other liabilities	(1,073)	(1,319)
Noncontrolling interests	(3,381)	(4,178)
The Company’s net interests in consolidated investment vehicles	25,469	30,713
CLOs
Variable Interest Entity [Line Items]
Cash and cash equivalents	40,327	82,823
Investments	1,722,625	1,555,879
Other assets	33,937	32,671
Notes payable	(1,569,663)	(1,457,435)
Securities purchased payable and other liabilities	(112,701)	(110,871)
Noncontrolling interests	(15,971)	(16,667)
The Company’s net interests in consolidated investment vehicles	98,554	86,400
Other
Variable Interest Entity [Line Items]
Cash and cash equivalents	464	18,489
Investments	23,688	7,250
Other assets	411	48
Notes payable	0	0
Securities purchased payable and other liabilities	(614)	(764)
Noncontrolling interests	(39)	0
The Company’s net interests in consolidated investment vehicles	$ 23,910	$ 25,023