Derivatives - Fair Values of Derivatives Reported on Consolidated Statements of Financial Condition (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Derivative Assets	$ 3,732	$ 1,993
Derivative Liabilities	198,417	182,223
Forward Foreign Currency Exchange Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets	3,314	1,993
Derivative Liabilities	4,846	2,792
Total Return Swaps and Other [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets	418
Derivative Liabilities	11,270	9,043
LFI and Other Similar Deferred Compensation Arrangements [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities	$ 182,301	$ 170,388