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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Net Revenue	$ 591,068	$ 626,481	$ 1,865,432	$ 2,139,117
Operating Expenses	538,695	487,800	1,591,711	1,614,668
Operating Income (Loss)	52,373	138,681	273,721	524,449
Total Assets	5,551,879		5,551,879		$ 4,997,241
Operating Segments [Member] | Financial Advisory Segment [Member]
Segment Reporting Information [Line Items]
Net Revenue	305,982	310,418	973,964	1,141,628
Operating Expenses	307,147	250,651	863,646	893,524
Operating Income (Loss)	(1,165)	59,767	110,318	248,104
Total Assets	1,075,851		1,075,851		859,306
Operating Segments [Member] | Asset Management Segment [Member]
Segment Reporting Information [Line Items]
Net Revenue	300,015	325,240	917,439	1,032,111
Operating Expenses	225,819	211,564	652,188	670,794
Operating Income (Loss)	74,196	113,676	265,251	361,317
Total Assets	703,744		703,744		728,220
Corporate [Member]
Segment Reporting Information [Line Items]
Net Revenue	(14,929)	(9,177)	(25,971)	(34,622)
Operating Expenses	5,729	25,585	75,877	50,350
Operating Income (Loss)	(20,658)	$ (34,762)	(101,848)	$ (84,972)
Total Assets	$ 3,772,284		$ 3,772,284		$ 3,409,715