Stock-Based Compensation - Stock option activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Options Outstanding
Outstanding at beginning of period (in shares)	7,455,795
Granted (in shares)	626,970
Cancelled/forfeited (in shares)	(498,114)
Outstanding at end of period (in shares)	7,584,651	7,455,795
Exercisable at end of period (in shares)	3,049,352
Weighted Average Exercise Price
Outstanding (in dollars per share)	$ 4.97	$ 5.52
Granted (in dollars per share)	0.55
Cancelled/forfeited (in dollars per share)	7.72
Exercisable at end of period (in dollars per share)	$ 6.68
Weighted Average Remaining Contractual Term (In years)
Outstanding (in years)	7 years 10 months 24 days	8 years
Exercisable at end of period (in years)	7 years
Aggregate Intrinsic Value
Outstanding (in dollars)	$ 314
Exercisable (in dollars)	$ 13