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, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Net Revenue	$ 573,518	$ 566,211	$ 1,760,359	$ 1,666,507
Operating Expenses	2,774	452,499	1,916,328	1,346,635
OPERATING INCOME (LOSS)	570,744	113,712	(155,969)	319,872
Total Assets	4,148,037		4,148,037		$ 3,332,236
Operating Segments [Member] | Financial Advisory Segment [Member]
Segment Reporting Information [Line Items]
Net Revenue	330,832	291,089	948,735	847,354
Operating Expenses	261,952	255,230	758,108	754,449
OPERATING INCOME (LOSS)	68,880	35,859	190,627	92,905
Total Assets	742,298		742,298		785,557
Operating Segments [Member] | Asset Management Segment [Member]
Segment Reporting Information [Line Items]
Net Revenue	264,581	291,967	850,226	848,695
Operating Expenses	179,155	191,501	554,738	552,499
OPERATING INCOME (LOSS)	85,426	100,466	295,488	296,196
Total Assets	515,544		515,544		588,403
Corporate [Member]
Segment Reporting Information [Line Items]
Net Revenue	(21,895)	(16,845)	(38,602)	(29,542)
Operating Expenses	(438,333)	5,768	603,482	39,687
OPERATING INCOME (LOSS)	416,438	$ (22,613)	(642,084)	$ (69,229)
Total Assets	$ 2,890,195		$ 2,890,195		$ 1,958,276