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Income Taxes - Components of deferred tax assets (Details) - USD ($) $ in Thousands | Dec. 31, 2021 | Dec. 31, 2020
--- | --- | ---
Deferred tax assets: |  |
Net operating losses | $ 106,055 | $ 64,259
Tax credit carryforwards | 12,424 | 5,670
Accrued expenses | 6,892 | 4,058
Lease liabilities | 3,698 | 3,166
Licensed technology | 2,775 | 1,534
Deferred revenue | 1,076 | 1,088
Depreciation | 493 | 502
Other | 71 | 84
Total gross deferred tax assets | 133,484 | 80,361
Valuation allowance | (130,051) | (77,375)
Net deferred tax assets less valuation allowance | 3,433 | 2,986
Deferred tax liabilities |  |
Right-of-use assets | (3,433) | (2,986)
Total gross deferred tax liabilities | (3,433) | (2,986)
Net deferred taxes | $ 0 | $ 0

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