Income taxes (Detail) - USD ($)	3 Months Ended	6 Months Ended
Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Income tax benefit, due to deferred tax liability as part of business acquisition	$ 100,000	$ 0	$ 10,600,000	$ 0

Represents the amount of income tax beneft due to the deferred tax liability as a part of business acquisition.

No definition available.

Name:	twst_BusinessAcquisitionIncomeTaxBenefitDueToDeferredTaxLiability
Namespace Prefix:	twst_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration