Segment Information - Segment's Contribution with Respect to Net Revenue, Operating Expenses, Operating Income (Loss) and Total Assets (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net Revenue	$ 717,180	$ 534,680	$ 1,340,644	$ 1,032,898
Operating Expenses	544,679	421,444	1,017,946	821,285
Operating Income (Loss)	172,501	113,236	322,698	211,613
Total Assets	4,769,762		4,769,762		$ 4,556,508
Operating Segments [Member] | Financial Advisory Segment [Member]
Segment Reporting Information [Line Items]
Net Revenue	410,882	286,965	746,694	552,979
Operating Expenses	313,719	233,727	576,470	460,805
Operating Income (Loss)	97,163	53,238	170,224	92,174
Total Assets	985,239		985,239		907,035
Operating Segments [Member] | Asset Management Segment [Member]
Segment Reporting Information [Line Items]
Net Revenue	309,878	254,126	593,241	499,885
Operating Expenses	215,901	182,702	404,652	357,863
Operating Income (Loss)	93,977	71,424	188,589	142,022
Total Assets	624,973		624,973		645,653
Corporate [Member]
Segment Reporting Information [Line Items]
Net Revenue	(3,580)	(6,411)	709	(19,966)
Operating Expenses	15,059	5,015	36,824	2,617
Operating Income (Loss)	(18,639)	$ (11,426)	(36,115)	$ (22,583)
Total Assets	$ 3,159,550		$ 3,159,550		$ 3,003,820