Income Taxes - Deferred Tax (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Income Taxes
Income tax liabilities	$ 0	$ 0
Federal net operating losses	3,445	3,840
State net operating losses	972	1,300
Stock based compensation	860	552
Federal and state tax credits	1,254	366
Capitalized research and development costs	8,288
Accrued expense	432	203
Total gross deferred tax assets	15,251	6,261
Less: valuation allowance	$ (15,251)	$ (6,261)

Carrying amount as of the balance sheet date of the unpaid sum of the known and estimated amounts payable to satisfy all domestic and foreign income tax obligations due. This amount is the total of current and noncurrent accrued income taxes.

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