Stockholders' Equity - Summary of the Share Activity Under the 2015 Plan (Details) - 2015 Equity Incentive Plan - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Number of Shares
Outstanding at the beginning (in shares)	3,976
Granted (in shares)	57
Exercised (in shares)	(34)
Forfeited (in shares)	(167)
Expired (in shares)	(358)
Outstanding at the end (in shares)	3,474	3,976
Expected to vest (in shares)	3,474
Exercisable (in shares)	3,077
Weighted Average Exercise Price
Outstanding at the beginning (in dollars per share)	$ 6.20
Granted (in dollars per share)	0.61
Exercised (in dollars per share)	0.86
Forfeited (in dollars per share)	5.17
Expired (in dollars per share)	5.41
Outstanding at the end (in dollars per share)	6.29	$ 6.20
Expected to vest (in dollars per share)	6.29
Exercisable (in dollars per share)	$ 6.50
Weighted Average Remaining Term
Weighted Average Remaining Term (in years)	2 years 10 months 20 days	3 years 9 months 18 days
Vested and expected to vest (in years)	2 years 10 months 20 days
Exercisable (in years)	2 years 2 months 1 day
Aggregate Intrinsic Value
Outstanding	$ 0	$ 0
Expected to vest	0
Exercisable	$ 0