Derivatives - Fair Values of Derivatives Reported on Condensed Consolidated Statements of Financial Condition (Detail) - USD ($) $ in Thousands		Jun. 30, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Derivative Assets		$ 6,652	$ 1,395
Derivative Liabilities		275,773	236,273
Forward Foreign Currency Exchange Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets		582	1,395
Derivative Liabilities		912	1,720
Total Return Swaps and Other [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets	[1]	6,070
Derivative Liabilities	[1]		8,527
LFI and Other Similar Deferred Compensation Arrangements [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities		$ 274,861	$ 226,026

[1] For total return swaps, amounts represent the netting of gross derivative assets and liabilities of $6,584 and $514 as of June 30, 2020, respectively, and $152 and $8,679 as of December 31, 2019, respectively, for contracts with the same counterparty under legally enforceable master netting agreements. Such amounts are recorded “net” in “other assets” and “other liabilities” as of June 30, 2020 and December 31, 2019, respectively.