Income Taxes - Deferred Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets:
Operating loss and credit carryforwards	$ 16,611	$ 15,217
Capitalized research and development	1,470	1,873
Stock-based compensation	1,284	1,078
Accrual for contingency matter	888
Lease liabilities	46	50
Excess book over tax depreciation	21	34
Total deferred tax assets	20,320	18,252
Less: valuation allowance	(20,274)	(18,200)
Deferred tax assets	46	52
Deferred tax liability:
Operating lease assets	(46)	(52)
Total deferred tax liability	$ (46)	$ (52)