Fair Value of Financial Instruments - Financial Instruments Not Measured at Fair Value (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Fair Value of Financial Instruments
Receivable from brokers and dealers and clearing organizations	$ 11,632	$ 0
Deposits with clearing organizations	23,906	20,523
Accounts receivable	142,676	129,937
Total assets measured at fair value	1,106,916	657,572
Payable to brokers and dealers and clearing organizations	11,264	0
Equity investment without readily determinable fair value	20,000	21,100
Income (loss) from investments	(1,000)	0	$ 0
Fair Value, Nonrecurring
Fair Value of Financial Instruments
Cash and restricted cash	151,313	318,495
Receivable from brokers and dealers and clearing organizations	11,632	0
Deposits with clearing organizations	23,906	20,523
Accounts receivable	142,676	129,937
Other assets – Memberships in clearing organizations	2,406	2,392
Total assets measured at fair value	331,933	471,347
Payable to brokers and dealers and clearing organizations	11,264	0
Total	11,264	0
Quoted Prices in active Markets for Identical Assets (Level 1)
Fair Value of Financial Instruments
Total assets measured at fair value	1,106,916	654,553
Quoted Prices in active Markets for Identical Assets (Level 1) \| Fair Value, Nonrecurring
Fair Value of Financial Instruments
Cash and restricted cash	151,313	318,495
Receivable from brokers and dealers and clearing organizations	0	0
Deposits with clearing organizations	23,906	20,523
Accounts receivable	0	0
Other assets – Memberships in clearing organizations	0	0
Total assets measured at fair value	175,219	339,018
Payable to brokers and dealers and clearing organizations	0	0
Total	0	0
Significant Observable Inputs (Level 2)
Fair Value of Financial Instruments
Total assets measured at fair value	0	3,019
Significant Observable Inputs (Level 2) \| Fair Value, Nonrecurring
Fair Value of Financial Instruments
Cash and restricted cash	0	0
Receivable from brokers and dealers and clearing organizations	11,632	0
Deposits with clearing organizations	0	0
Accounts receivable	142,676	129,937
Other assets – Memberships in clearing organizations	0	0
Total assets measured at fair value	154,308	129,937
Payable to brokers and dealers and clearing organizations	11,264	0
Total	11,264	0
Significant Unobservable Inputs (Level 3)
Fair Value of Financial Instruments
Total assets measured at fair value	0	0
Significant Unobservable Inputs (Level 3) \| Fair Value, Nonrecurring
Fair Value of Financial Instruments
Cash and restricted cash	0	0
Receivable from brokers and dealers and clearing organizations	0	0
Deposits with clearing organizations	0	0
Accounts receivable	0	0
Other assets – Memberships in clearing organizations	2,406	2,392
Total assets measured at fair value	2,406	2,392
Payable to brokers and dealers and clearing organizations	0	0
Total	0	0
Total Fair Value \| Fair Value, Nonrecurring
Fair Value of Financial Instruments
Cash and restricted cash	151,313	318,495
Receivable from brokers and dealers and clearing organizations	11,632	0
Deposits with clearing organizations	23,906	20,523
Accounts receivable	142,676	129,937
Other assets – Memberships in clearing organizations	2,406	2,392
Total assets measured at fair value	331,933	471,347
Payable to brokers and dealers and clearing organizations	11,264	0
Total	$ 11,264	$ 0

Amount payable to other broker-dealer and clearing organization, including, but not limited to, security failed-to-receive, deposit received for security loaned, open transaction, and floor-brokerage payable.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher SEC
-Name Rule 15c3-1
-Number 240
-Section 15c3-1

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Account receivable excluding receivable from brokers and dealers and clearing organizations, net of allowance.

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Restricted Cash and Cash Equivalents, Fair Value Disclosure

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
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The amount of securities on deposit with clearing organizations and other entities which provide services necessary to operations of the Company. This item would include, for instance, securities advanced as refundable collateral for securities borrowed.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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Amount of realized gain (loss) from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 4
-URI https://asc.fasb.org/extlink&oid=126980263&loc=SL75117546-209714

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
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Amount of investment in equity security without readily determinable fair value.

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-Publisher FASB
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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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Fair value of financial and nonfinancial obligations.

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Amount receivable from broker-dealers and clearing organizations, including, but not limited to, securities failed-to-deliver, certain deposits for securities borrowed, open transactions, good faith and margin deposits, commissions and floor brokerage receivables.

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Amount of right to receive cash and securities on deposit with clearing organizations. Clearing organizations perform post trade processing and trade comparisons among numerous broker-dealers and act as settlement agents between buying and selling broker-dealers.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI https://asc.fasb.org/subtopic&trid=2176284

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