Income Taxes - Rate reconciliation (Details)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Rate reconciliation
Federal tax benefit at statutory rate	(21.00%)	(21.00%)	(21.00%)
State rate, net of federal benefit	(3.10%)	(3.50%)	(4.20%)
Permanent differences	0.6	0.2	0.6
Research and development		0.40%	0.70%
Change in valuation allowance	23.40%	24.20%	24.00%
Other	0.10%	(0.30%)	(0.10%)
Total tax provision