Income Taxes - Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	21.00%	21.00%
State taxes, net of federal benefit	5.90%	5.90%
Federal and state research and development tax credits	3.70%	4.70%
Other	0.10%	0.30%
Nondeductible items	(1.00%)	(1.30%)
Change in valuation allowance	(29.70%)	(30.60%)
Effective income tax rate	0.00%	0.00%