XML 77 R39.htm IDEA: XBRL DOCUMENT v3.20.1
Income Taxes - Effective income tax rate reconciliation (Details)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Income Taxes    
Federal statutory rate 21.00% 21.00%
State tax rate, net of federal benefit 0.10% 0.30%
Permanent differences (0.20%) (0.80%)
Research & development tax credits 3.00% 2.80%
Prior period adjustments and other (0.60%) (2.60%)
Change in valuation allowance (23.30%) (20.70%)
Effective income tax rate 0.00% 0.00%