Share-based compensation - Activity (Details)	1 Months Ended	12 Months Ended
	Aug. 31, 2020 USD ($) employee shares	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Sep. 30, 2020 $ / shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Share-based Payment Arrangement, Expense | $	$ 0	$ 621,000	$ 14,000
Fair value of option price per share				$ 8.69
Two Officers [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options, Granted | shares	92,169
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Number Of Employees Granted Stock Options | employee	2
The Plans
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options, Beginning balance | shares		583,622
Options, Granted | shares		1,168,618
Options, Forfeited | shares		(152,109)
Options, Exercised | shares		(127,291)
Options, Ending balance | shares		1,472,840	583,622
Options, Exercisable | shares		632,524
Options, Vested and expected to vest | shares		1,472,840
Weighted Average Exercise price
Beginning price		$ 0.47
Granted		4.90
Forfeited		8.90
Exercised		0.16
Ending price		3.14	$ 0.47
Exercisable		0.89
Vested and expected to vest		$ 3.14
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted Average Remaining Contractual Term		8 years 6 months 3 days	6 years 3 months 18 days
Weighted Average Remaining Contractual Term, Exercisable		7 years 4 months 17 days
Weighted Average Remaining Contractual Term, Vested and expected to vest		8 years 6 months 3 days
Weighted average grant date fair value		$ 3.71	$ 0.24
Intrinsic value, exercised | $		$ 1,200,000
Intrinsic value, outstanding | $		$ 10,100,000	$ 200,000