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Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Fair Value Measurements [Line Items]
Realized gains or losses recognized on the sale or maturity of available-for-sale securities	$ 0	$ 0	$ 0	$ 0

X

- Definition

Fair value measurements.

+ References

No definition available.

+ Details

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Namespace Prefix:	sndx_
Data Type:	xbrli:stringItemType
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X

- Definition

Amount of realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-9

+ Details

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