Commitments and Contingencies - Narratives (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Commitments and Contingencies
Financing liability		$ 872
Accrued settlement		200
Lab equipment
Commitments and Contingencies
Proceeds from sale and leaseback transactions		1,200	$ 1,600
Financing liability		1,900
Penn License Agreement | Penn
Commitments and Contingencies
Annual payments to be made		25,000
Additional milestone payments for first CAR-M product		1,700
Penn License Agreement | Penn | Maximum
Commitments and Contingencies
Milestone payments		10,900
Additional milestone payments		$ 30,000
Novartis Agreement
Commitments and Contingencies
Agreement term	5 years
Renewal term	1 year
Amount payable per calendar year for reserved capacity	$ 1,000
Termination fee payable	$ 4,000