Derivatives - Fair Values of Derivatives Reported on Condensed Consolidated Statements of Financial Condition (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Derivatives, Fair Value [Line Items]
Derivative Assets	$ 1,254	$ 536
Derivative Liabilities	395,424	314,485
Forward Foreign Currency Exchange Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets	1,254	536
Derivative Liabilities	340	333
Total Return Swaps and Other [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities	718	2,752
Warrant [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities	11,500
LFI and Other Similar Deferred Compensation Arrangements [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities	$ 382,866	$ 311,400