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								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Net Revenue	$ 691,565	$ 608,908	$ 534,680	$ 498,218	$ 593,249	$ 573,518	$ 609,092	$ 577,749	$ 2,333,371	$ 2,353,608	$ 2,300,447
Operating Expenses	534,709	459,916	421,444	399,841	453,900	2,774	1,410,468	503,086	1,815,910	2,370,228	1,780,982
Operating Income (Loss)	156,856	$ 148,992	$ 113,236	$ 98,377	139,349	$ 570,744	$ (801,376)	$ 74,663	517,461	(16,620)	519,465
Total Assets	4,556,508				4,477,774				4,556,508	4,477,774	3,325,329
Depreciation and amortization of property									33,264	32,785	34,464
Operating Segments [Member] | Financial Advisory Segment [Member]
Segment Reporting Information [Line Items]
Net Revenue									1,301,044	1,279,628	1,206,734
Operating Expenses									1,017,055	1,005,837	977,681
Operating Income (Loss)									283,989	273,791	229,053
Total Assets	907,035				763,374				907,035	763,374	785,557
Depreciation and amortization of property									5,661	4,412	4,826
Operating Segments [Member] | Asset Management Segment [Member]
Segment Reporting Information [Line Items]
Net Revenue									1,051,316	1,111,105	1,134,595
Operating Expenses									769,737	736,798	749,345
Operating Income (Loss)									281,579	374,307	385,250
Total Assets	645,653				640,034				645,653	640,034	588,403
Depreciation and amortization of property									3,666	2,957	2,610
Corporate [Member]
Segment Reporting Information [Line Items]
Net Revenue									(18,989)	(37,125)	(40,882)
Operating Expenses									29,118	627,593	53,956
Operating Income (Loss)									(48,107)	(664,718)	(94,838)
Total Assets	$ 3,003,820				$ 3,074,366				3,003,820	3,074,366	1,951,369
Depreciation and amortization of property									$ 23,937	$ 25,416	$ 27,028