Derivatives - Fair Values of Derivatives Reported on Condensed Consolidated Statements of Financial Condition (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Derivative Assets	$ 11,607	$ 3,732
Derivative Liabilities	214,975	198,417
Forward Foreign Currency Exchange Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets	6,379	3,314
Derivative Liabilities	2,535	4,846
Total Return Swaps and Other [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets	5,228	418
Derivative Liabilities	24	11,270
LFI and Other Similar Deferred Compensation Arrangements [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities	$ 212,416	$ 182,301