Consolidation - Condensed Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Variable Interest Entity [Line Items]
Cash and cash equivalents	$ 233,465	$ 82,687	$ 97,384	$ 203,304
Noncontrolling interests	(4,178)	(37,266)	$ (73,864)	$ (23,071)
VOEs
Variable Interest Entity [Line Items]
Cash and cash equivalents	820	1,859
Investments	34,623	99,247
Other assets	767	2,211
Notes payable	0	0
Securities purchased payable and other liabilities	(1,319)	(2,310)
Noncontrolling interests	(4,178)	(12,505)
The Company’s net interests in consolidated investment products	30,713	88,502
CLOs
Variable Interest Entity [Line Items]
Cash and cash equivalents	82,823	14,449
Investments	1,555,879	346,967
Other assets	32,671	5,888
Notes payable	(1,457,435)	(328,761)
Securities purchased payable and other liabilities	(110,871)	(12,534)
Noncontrolling interests	(16,667)	0
The Company’s net interests in consolidated investment products	86,400	26,009
Other
Variable Interest Entity [Line Items]
Cash and cash equivalents	18,489	2,775
Investments	7,250	42,828
Other assets	48	1,059
Notes payable	0	0
Securities purchased payable and other liabilities	(764)	(1,799)
Noncontrolling interests	0	(24,761)
The Company’s net interests in consolidated investment products	$ 25,023	$ 20,102