Income Taxes - Reconciliation (Details)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Effective income tax rate
Tax effected at statutory rate	21.00%	21.00%
State taxes	7.20%	6.60%
Stock compensation	(1.70%)	(1.70%)
Non deductible expenses	(0.40%)	(0.10%)
Federal research and development credits	7.80%	5.90%
Change in valuation allowance	(33.90%)	(31.70%)

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the valuation allowance for deferred tax assets.

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Percentage of difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operation, attributable to expense for award under share-based payment arrangement. Excludes expense determined to be nondeductible upon grant or after for award under share-based payment arrangement.

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