Consolidation - Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Cash and cash equivalents	$ 386,063	$ 82,687	$ 179,273	$ 97,384
Noncontrolling interests	(67,227)	(37,266)	$ (30,301)	$ (73,864)
VOEs
Variable Interest Entity [Line Items]
Cash and cash equivalents	756	1,859
Investments	33,053	99,247
Other assets	790	2,211
Notes payable	0	0
Securities purchased payable and other liabilities	(1,422)	(2,310)
Noncontrolling interests	(3,821)	(12,505)
The Company’s net interests in consolidated investment vehicles	29,356	88,502
CLOs
Variable Interest Entity [Line Items]
Cash and cash equivalents	217,747	14,449
Investments	1,494,992	346,967
Other assets	34,847	5,888
Notes payable	(1,455,932)	(328,761)
Securities purchased payable and other liabilities	(188,270)	(12,534)
Noncontrolling interests	(16,487)	0
The Company’s net interests in consolidated investment vehicles	86,897	26,009
Other
Variable Interest Entity [Line Items]
Cash and cash equivalents	3,415	2,775
Investments	67,682	42,828
Other assets	1,303	1,059
Notes payable	0	0
Securities purchased payable and other liabilities	(1,620)	(1,799)
Noncontrolling interests	(63,406)	(24,761)
The Company’s net interests in consolidated investment vehicles	$ 7,374	$ 20,102