XML 25 R53.htm IDEA: XBRL DOCUMENT v3.20.1
Income Taxes - Reconciliation of Income Tax Expense (Benefit) (Details) - USD ($)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Reconciliation of income tax expense (benefit)      
Income tax expense (benefit) $ 0 $ 0 $ 0
U.S. federal statutory income tax rate 21.00% 21.00% 34.00%
State taxes, net of federal benefit 13.50% 13.10% 10.00%
Stock based compensation - Excess tax benefit 1.20% 1.10% (1.00%)
Other permanent differences (0.10%) (1.30%) (1.90%)
Tax credit 4.20% 6.30% 7.70%
US federal taz rate change - tax reform     (25.4)
Change in valuation allowance (39.80%) (40.20%) (23.40%)