Income Taxes - Reconciliation (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of federal statutory income tax rate to the Company’s effective income tax rate
Expected income tax benefit at the federal statutory rate (as a percent)	21.00%	21.00%
State taxes, net of federal benefit (as a percent)	7.00%	6.50%
Research and development credit, net (as a percent)	4.90%	7.20%
Non-deductible items (as a percent)	(0.50%)	(2.20%)
Prior year provision to return adjustments (as a percent)	(2.50%)	(7.70%)
Other (as a percent)		0.30%
Change in valuation allowance (as a percent)	(29.90%)	(25.10%)