Revenue Recognition - Representation of Performance Obligations Relate to Nature, Amount, Timing and Uncertainty of Revenue and Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Net Revenue	$ 754,698	$ 623,464
Financial Advisory Segment [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Net Revenue	409,121
Asset Management Segment [Member]
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Net Revenue	354,283
Asset Management Segment [Member] | Management Fees And Other
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Net Revenue	348,684
Asset Management Segment [Member] | Incentive Fees
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Net Revenue	$ 5,599