Equity Incentive Plans - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended				6 Months Ended	12 Months Ended
	Jun. 18, 2014	Jan. 31, 2024	Dec. 31, 2022	Jan. 31, 2022	Jan. 31, 2021	Jun. 30, 2015	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Nov. 30, 2016
Equity Incentive Plans
Common stock closing price (in dollars per share)							$ 6.20
Intrinsic value of options exercised							$ 1,100	$ 30	$ 1,700
Weighted-average grant-date estimated fair value of options granted (in dollars per share)							$ 2.36	$ 0.63	$ 3.92
Issuance of common stock for services							$ 337	$ 390	$ 190
2014 Plan
Equity Incentive Plans
Number of shares initially authorized (in shares)	1,400,000
Number of shares added to initial reserve	35,000
Common stock reserved for future issuance (in shares)	1,500,000						2,500,000
Potential increase to shares reserved for inclusion of forfeited or unexercised options from prior plan	1,200,000
Potential increase in shares reserved as a percentage of shares outstanding	4.00%
Maximum shares to be issued upon exercise of incentive stock options	10,700,000
Inducement Plan
Equity Incentive Plans
Number of shares added to initial reserve			3,000,000	2,000,000	500,000
Common stock reserved for future issuance (in shares)							900,000			1,000,000
Share of common stock subject to issued inducement grants							6,000,000
Inducement Plan | Subsequent event
Equity Incentive Plans
Number of shares added to initial reserve		5,800,000
ESPP
Equity Incentive Plans
Common stock reserved for future issuance (in shares)	200,000						1,100,000
Potential increase in shares reserved as a percentage of shares outstanding	1.00%
Weighted-average grant-date estimated fair value of options granted (in dollars per share)							$ 1.85	$ 0.63	$ 2.12
Dividend yield							0.00%	0.00%	0.00%
Issuance of common stock for services (in shares)							436,000	308,000	387,000
Maximum shares to be issued under ESPP	2,200,000
Stock options
Equity Incentive Plans
Dividend yield							0.00%	0.00%	0.00%
Stock options | 2008 Plan
Equity Incentive Plans
Vesting period (in years)						4 years
RSUs
Equity Incentive Plans
Estimated fair value of RSUs vested							$ 3,500	$ 2,600	$ 800
Number of shares granted							3,269,000
Number of shares vested							942,000
Board of directors
Equity Incentive Plans
Issuance of common stock for services (in shares)							100,000	700,000	26,000
Issuance of common stock for services							$ 300	$ 400	$ 200