Derivatives - Fair Values of Derivatives Reported on Condensed Consolidated Statements of Financial Condition (Parenthetical) (Detail) - Total Return Swaps [Member] - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Gross derivative assets	$ 3,401	$ 469
Gross derivative liability	937	11,321
Cash collateral pledged for total return swaps	$ 2,316	$ 17,616

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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