Equity Incentive Plans - Stock-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Equity Incentive Plans
Total stock-based compensation expense	$ 1,981	$ 2,493	$ 3,338
Common stock options
Equity Incentive Plans
Total stock-based compensation expense	$ 1,981	$ 2,492	$ 3,338
Assumptions used to compute employee stock based compensation under the Black-Scholes option pricing model
Expected dividend yield (as a percent)	0.00%	0.00%	0.00%
Expected life (in years)	6 years 3 months	6 years 3 months	6 years 3 months
Unrecorded deferred stock-based compensation
Unrecorded deferred stock-based compensation balance related to stock options	$ 1,400
Weighted-average amortization period over which cost is expected to be recognized	2 years 9 months 18 days
Weighted average grant date fair value of options granted (in dollars per share)	$ 2.64
Common stock options | Cost of product revenues
Equity Incentive Plans
Total stock-based compensation expense	$ 107	$ 133	$ 271
Common stock options | Research and development
Equity Incentive Plans
Total stock-based compensation expense	358	372	490
Common stock options | Selling and marketing
Equity Incentive Plans
Total stock-based compensation expense	102	155	148
Common stock options | General and administrative
Equity Incentive Plans
Total stock-based compensation expense	$ 1,414	$ 1,832	$ 2,429
Common stock options | Minimum
Assumptions used to compute employee stock based compensation under the Black-Scholes option pricing model
Risk-free interest rate (as a percent)	3.87%	1.71%	0.66%
Expected volatility (as a percent)	115.90%	107.00%	105.00%
Common stock options | Maximum
Assumptions used to compute employee stock based compensation under the Black-Scholes option pricing model
Risk-free interest rate (as a percent)	3.90%	4.22%	1.51%
Expected volatility (as a percent)	118.60%	118.00%	106.00%
Unvested restricted stock units
Unrecorded deferred stock-based compensation
Unrecorded deferred stock-based compensation balance related to stock options	$ 300
Weighted-average amortization period over which cost is expected to be recognized	3 years 1 month 9 days