Debt - Additional Information (Short Term Debt) (Detail) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Short-term Debt [Line Items]
Securities sold under agreements to repurchase	$ 69,600,000	$ 43,700,000
Line of Credit
Short-term Debt [Line Items]
Overnight federal funds borrowed	0	85,000,000.0
Overnight federal funds lines available for borrow	215,000,000.0
Line of Credit \| Federal Home Loan Bank of New York
Short-term Debt [Line Items]
Overnight borrowings	100,000,000.0	200,000,000.0
Federal Reserve Bank of New York \| Line of Credit
Short-term Debt [Line Items]
Borrowings with the Federal Reserve Bank	0	$ 0
Short Term and Long Term Mortgage Backed Securities Sold Under Agreements To Repurchase
Short-term Debt [Line Items]
Securities Received as Collateral	$ 73,400,000

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Federal Reserve Bank, Advances, Amount Of Advances By Branch

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Amount of short term borrowing where a bank borrows, at the federal funds rate, from another bank.

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The carrying value as of the balance sheet date of the assets received as collateral against securities loaned to other broker-dealers. Borrowers of securities generally are required to provide collateral to the lenders of securities, commonly cash but sometimes other securities or standby letters of credit, with a value slightly higher than that of the securities borrowed. In instances where the entity is permitted to sell or re-pledge these securities, the entity reports the fair value of the collateral received and the related obligation to return the collateral as a liability.

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Amount, after the effects of master netting arrangements, of funds outstanding borrowed in the form of a security repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same securities at a date certain for a specified price. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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