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Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended
	Jan. 01, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Cash and cash equivalents maturity period, maximum			90 days
Short-term lease exception - Lease term			12 months
Purchase of securities owned, a fair value			$ 97,570	$ 34,683
Proceeds from the sale of securities owned, at fair value			$ 10,976	18,122
Adjustment [Member]
Amounts collected on behalf of third parties		$ 891		2,380
Purchase of securities owned, a fair value				34,683
Proceeds from the sale of securities owned, at fair value				$ 18,122
Accounting Standards Update 2020-06 [Member]
Reduction of interest expense per quarter	$ 420
Reduction of accumulated deficit	616
Increase in carrying value of convertible notes	4,088
Decrease in additional paid in capital	3,682
Decrease in deferred tax liability	$ 1,022

X

- Definition

Term of lessee's operating lease renewal, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
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-Section 50
-Paragraph 3
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- Definition

Amount of cash outflow to acquire investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI), classified as investing activity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=123583714&loc=SL75117360-209713

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-Section 45
-Paragraph 19
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- Definition

Amount of cash inflow from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI), classified as investing activity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 19
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3444-108585

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- Definition

Cash and cash equivalents criteria maturity period.

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- Definition

Decrease in additional paid in capital.

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- Definition

Decrease in deferred tax liability.

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- Definition

Increase in carrying value of convertible notes.

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- Definition

Increase in retained earnings.

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- Definition

Reclassification towards amount collected on behalf of third parties.

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- Definition

Reduction of interest expense per quarter.

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