Cash and Cash Equivalents and Restricted Cash - Summary of Reconciliation of Cash and Cash Equivalents with Restricted or Segregated Cash (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Cash And Cash Equivalents [Line Items]
Cash and cash equivalents	$ 432,715	$ 460,858
Cash segregated under federal regulations	50,134	50,059
Deposits with clearing organizations and broker-dealers	80,862	97,043
Total	563,801	608,050
Cash and Cash Equivalents [Member]
Cash And Cash Equivalents [Line Items]
Cash and cash equivalents	432,715	460,858
Cash Segregated under Federal Regulations and Other [Member]
Cash And Cash Equivalents [Line Items]
Cash segregated under federal regulations	50,134	50,059
Receivables from Broker-Dealers, Clearing Organizations and Customers [Member]
Cash And Cash Equivalents [Line Items]
Deposits with clearing organizations and broker-dealers	80,862	97,043
Prepaid Expenses and Other Assets [Member]
Cash And Cash Equivalents [Line Items]
Other deposits	$ 90	$ 90

Other deposits.

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- Definition

Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

+ References

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- Definition

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.

+ References

No definition available.

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- Definition

Amount of cash subject to withdrawal restrictions, restricted deposits held as compensating balances, and cash and securities segregated in compliance with regulations (such as cash deposited in a special reserve account for the exclusive benefit of customers).

+ References

No definition available.

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- Definition

Amount of cash and cash equivalents, and cash and cash equivalents restricted to withdrawal or usage. Excludes amount for disposal group and discontinued operations. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

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- Definition

This is the amount of cash advanced as security in return for borrowing securities from another party.

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