Income Taxes	12 Months Ended
	Dec. 31, 2021
Income Taxes [Abstract]
Income Taxes	11. Income Taxes Income (loss) before income taxes (in thousands): Year Ended December 31, 2021 2020 2019Domestic $ (63,660) $ (49,851) $ (46,971)Foreign — — — $ (63,660) $ (49,851) $ (46,971) The components of the provision for income taxes are as follows (in thousands): December 31, 2021 2020 2019Current Federal $ — $ — $ —State 3 3 3Foreign — — —Total current 3 3 3 Deferred Federal — — —State — — —Foreign — — —Total deferred — — — Total provision for income taxes $ 3 $ 3 $ 3 The provision for income taxes differs from the amount estimated by applying the statutory federal income tax rate to income (loss) before taxes as follows: Year Ended December 31, 2021 2020 2019Federal tax at statutory rate 21.0% 21.0% 21.0%State tax (benefit) at statutory rate 8.4 8.4 (5.0) Research and development credits 1.9 2.1 2.0 Change in valuation allowance (26.8) (43.3) (18.0) Deferred adjustment — 8.5 — Change in tax rate — 4.2 — Uncertain Tax Position (2.3) — — Other (2.2) (0.8) — Provision for income taxes —% —% —% Note that for presentation purposes, the 2019 percentages have been changed to present the opposite value from what was previously disclosed to allow for proper comparability to current year percentages. Deferred income taxes reflect the impact of carryforwards and temporary differences between the amounts of assets and liabilities for financial reporting purposes and such amounts as measured by tax laws. The carryforwards and temporary differences, which give rise to a significant portion of the Company’s deferred tax asset (liability) as of December 31, 2021 and 2020, are as follows (in thousands): December 31, 2021 2020Deferred tax assets Accruals $ 1,034 $ 894Net operating loss carryforwards 49,246 36,531Tax credit carryforwards 6,611 5,431Stock-based compensation 12,188 9,391Lease liability under ASC 842 3,182 3,339Gross deferred tax assets 72,261 55,586Valuation allowance (69,006) (51,973)Total deferred tax assets 3,255 3,613 Deferred tax liabilities Intangibles (365) (486)ROU asset under ASC 842 (2,862) (3,096)Fixed assets (28) (31)Total deferred tax liabilities (3,255) (3,613) Net deferred tax assets/(liabilities) $ — $ — The Company’s unrecognized tax benefits as of December 31, 2021, 2020, and 2019 were $5.1 million, $2.5 million, and $1.5 million, respectively. If recognized, none of the unrecognized tax benefits would impact income tax expense to the extent that the Company continues to maintain a full valuation allowance against its deferred tax assets. A reconciliation of the beginning and ending amounts of unrecognized tax benefit is as follows (in thousands): December 31, 2021 2020 2019Unrecognized tax benefits at beginning of year $ 2,491 $ 1,470 $ 877Increases related to current year tax positions 2,649 1,021 593Unrecognized tax benefits at end of year $ 5,140 $ 2,491 $ 1,470 The Company’s policy is to recognize interest and penalties related to income taxes as components of interest expense and other expense, respectively. The Company did not accrue interest and penalties related to unrecognized tax benefits as of December 31, 2021 and does not anticipate any significant change within twelve months of this reporting date. The Company’s valuation allowance increased by $17.0 million in the year ended December 31, 2021 and increased by $21.6 million in the year ended December 31, 2020. As of December 31, 2021, the Company had federal and state net operating loss (“NOL”) carryforwards of $173.7 million and $163.4 million, respectively, which begin to expire in 2034. Of the total federal NOL carryforward of $173.7 million, approximately $148.0 million is carried forward indefinitely but is limited to 80% of the taxable income. As of December 31, 2021, the Company had approximately $5.3 million and $5.0 million of U.S. federal and California research and development (“R&D”) credits, respectively. The federal R&D credits begin to expire in 2035 and the California R&D credits have an indefinite carryforward period. The Company is subject to taxation in the United States for Federal and for State, within various states in which the Company operates. All jurisdictions and tax years currently remain open for IRS and state taxing authorities’ examination. As of December 31, 2021, the Company was not under examination by the Internal Revenue Service or any state tax jurisdiction. Internal Revenue Code Section 382 ownership change generally occurs if one or more stockholders or groups of stockholders who own at least 5% of our stock increase their ownership by more than 50 percentage points over their lowest ownership percentage within a rolling three-year period. Similar rules may apply under state tax laws. The Company is not aware of any ownership changes in this financial period ending on December 31, 2021.