Income Taxes - Deferred tax asset (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Deferred tax assets:
Net operating loss carryforwards	$ 25,660	$ 23,719
Stock compensation and other	42	293
In process research and development	1,603	1,162
Accruals and reserves	64	6
Business interest expense disallowance	122	0
Section 174 capitalization	622	0
Tax credits	2,859	2,640
Total deferred tax assets	30,972	27,820
Less valuation allowance	(30,972)	(27,820)
Deferred tax assets, net of valuation allowance	$ 0	$ 0