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
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net Revenue	$ 623,464	$ 498,218
Operating Expenses	473,267	399,841
Operating Income (Loss)	150,197	98,377
Total Assets	4,385,258		$ 4,556,508
Operating Segments [Member] | Financial Advisory Segment [Member]
Segment Reporting Information [Line Items]
Net Revenue	335,812	266,014
Operating Expenses	262,751	227,078
Operating Income (Loss)	73,061	38,936
Total Assets	828,374		907,035
Operating Segments [Member] | Asset Management Segment [Member]
Segment Reporting Information [Line Items]
Net Revenue	283,363	245,759
Operating Expenses	188,751	175,161
Operating Income (Loss)	94,612	70,598
Total Assets	572,915		645,653
Corporate [Member]
Segment Reporting Information [Line Items]
Net Revenue	4,289	(13,555)
Operating Expenses	21,765	(2,398)
Operating Income (Loss)	(17,476)	$ (11,157)
Total Assets	$ 2,983,969		$ 3,003,820