Astellas Agreements - Additional Information (Details) - USD ($)		1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Oct. 21, 2022	Oct. 31, 2022	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025	Dec. 31, 2025
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock, shares issued			325,883,880		325,883,880		285,051,648
Probability of option exercise		50.00%
Revenues			$ 0	$ 0	$ 0	$ 4,288,000
Rett Option
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenues							$ 5,500,000
Rett research and development activities
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenues				$ 0		$ 4,300,000
Astellas
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront Payment	$ 20,000,000
Transaction price		$ 36,100,000			36,059,000
Deferred revenue		$ 36,100,000
Astellas | Securities Purchase Agreement | Private Placement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock, shares issued	7,266,342	7,266,342
Aggregate gross proceeds	$ 30,000,000
Fair value of shares transferred, Value		$ 13,950,000
Share price		$ 1.92
Transaction price		$ 16,100,000
Difference of market value paid		$ 30,000,000
Astellas | TSHA-120
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront Payment					20,000,000
Transaction price					36,100,000
Astellas | TSHA-120 | Private Placement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price					16,100,000
Astellas | Rett research and development activities
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price					$ 28,257,000