Income Taxes - Components of Net Deferred Tax Assets (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Income Taxes
Capitalized research and development expenses	$ 7,822	$ 11,500
Net operating loss carryforwards	17,657	17,638
Research and development and other tax credit carryforwards	13,125	13,454
Stock compensation	4,778	5,158
Unearned revenue	2,817	3,462
Other	807	401
Total deferred tax assets	47,006	51,613
Valuation allowance	(47,006)	(51,613)
(Decrease) increase in the valuation allowance	$ (4,600)	$ (3,900)

Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from deferred income.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from in-process research and development costs expensed in connection with a business combination.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards.

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Amount, before allocation of valuation allowance, of deferred tax asset attributable to deductible temporary differences, classified as other.

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Amount, before allocation of a valuation allowances, of deferred tax assets attributable to deductible tax credit carryforwards including, but not limited to, research, foreign, general business, alternative minimum tax, and other deductible tax credit carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from share-based compensation.

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Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

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Amount of increase (decrease) in the valuation allowance for a specified deferred tax asset.

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