Consolidation - Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Cash and cash equivalents	$ 136,499	$ 234,282	$ 252,860	$ 83,671
Noncontrolling interests	(4,162)	(4,178)	$ (44,976)	$ (37,266)
VOEs
Variable Interest Entity [Line Items]
Cash and cash equivalents	978	820
Investments	36,702	34,623
Other assets	499	767
Notes payable	0	0
Securities purchased payable and other liabilities	(1,145)	(1,319)
Noncontrolling interests	(4,123)	(4,178)
The Company’s net interests in consolidated investment vehicles	32,911	30,713
CLOs
Variable Interest Entity [Line Items]
Cash and cash equivalents	54,757	82,823
Investments	1,572,898	1,555,879
Other assets	31,709	32,671
Notes payable	(1,460,177)	(1,457,435)
Securities purchased payable and other liabilities	(90,920)	(110,871)
Noncontrolling interests	(16,619)	(16,667)
The Company’s net interests in consolidated investment vehicles	91,648	86,400
Other
Variable Interest Entity [Line Items]
Cash and cash equivalents	0	18,489
Investments	24,485	7,250
Other assets	314	48
Notes payable	0	0
Securities purchased payable and other liabilities	(356)	(764)
Noncontrolling interests	(39)	0
The Company’s net interests in consolidated investment vehicles	$ 24,404	$ 25,023