Astellas Agreements - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended		3 Months Ended
	Oct. 21, 2022	Oct. 31, 2022	Mar. 31, 2021	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock, shares issued				187,018,275		186,960,193
Probability of option exercise		50.00%
Revenues				$ 3,411	$ 4,706
Deferred revenue				14,695		$ 18,106
TSHA-120
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront Payment			$ 5,500
Rett Option
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue				5,500
Rett research and development activities
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenues				3,400	$ 4,700
Deferred revenue				9,200
Astellas
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront Payment	$ 20,000
Transaction price		$ 36,100		36,059
Deferred revenue		$ 36,100
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
Fair value of shares transferred, Value		$ 13,950
Share price		$ 1.92
Transaction price		$ 16,100
Difference of market value paid		$ 30,000
Astellas | TSHA-120
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront Payment				20,000
Transaction price				36,100
Astellas | TSHA-120 | Private Placement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price				16,100
Astellas | Rett research and development activities
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price				$ 28,257