Summary of significant accounting policies - Concentration of Credit Risk (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) customer	Dec. 31, 2019 USD ($) customer
Concentration Risk [Line Items]
Cash, FDIC Insured Amount \| $	$ 250,000
Cash, Uninsured Amount \| $	$ 770,098	$ 627,676
Customer concentration risk \| Revenues
Concentration Risk [Line Items]
Number of customer representing more than 10% of revenues or trade accounts receivable	1	1
Number of customers	533
Customer concentration risk \| Trade accounts receivable
Concentration Risk [Line Items]
Number of customer representing more than 10% of revenues or trade accounts receivable	0	1