Share-Based Compensation - Stock option and restricted stock unit activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Amount, Outstanding	1,893,201
Amount, Granted	686,232
Amount, Outstanding	2,501,419	1,893,201
Weighted-average exercise price, Outstanding	$ 6.44
Weighted-average exercise price, Granted	2.08
Weighted-average exercise price, Outstanding	$ 4.35	$ 6.44
Biostage2013 Equity Incentive Plan [Member] | Stock Options [Member]
Amount, Outstanding	1,599,720
Amount, Granted	1,253,336
Amount, Canceled / forfeited	(520,453)
Amount, Outstanding	2,332,603	1,599,720
Amount, Options exercisable	1,074,760
Amount, Options vested and expected to vest	2,261,832
Weighted-average exercise price, Outstanding	$ 6.33
Weighted-average exercise price, Granted	2.15
Weighted-average exercise price, Canceled / forfeited	7.73
Weighted-average exercise price, Outstanding	3.93	$ 6.33
Weighted-average exercise price, Options exercisable	5.48
Weighted-average exercise price, Options vested and expected to vest	$ 3.83
Weighted-average contractual life, Outstanding	8 years 3 months 18 days	5 years 9 months 7 days
Weighted-average contractual life, Options exercisable	6 years 9 months 29 days
Outstanding at the end (in dollars)	$ 294
Exercisable at the end (in dollars)	$ 129