Share-based compensation - Activity (Details)	1 Months Ended	3 Months Ended		12 Months Ended
	Aug. 31, 2020 USD ($) employee shares	Mar. 31, 2021 USD ($) $ / shares shares	Mar. 31, 2020 USD ($) $ / shares	Dec. 31, 2020 $ / 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	$ 325,000	$ 146,000
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		1,472,840
Options, Granted | shares		183,000
Options, Forfeited | shares		(5,501)
Options, Exercised | shares		(14,270)
Options, Ending balance | shares		1,636,069		1,472,840
Options, Exercisable | shares		480,790
Options, Vested and expected to vest | shares		1,636,069
Weighted Average Exercise price
Beginning price		$ 3.14
Granted		31.83
Forfeited		8.10
Exercised		0.39
Ending price		6.36		$ 3.14
Exercisable		1.42
Vested and expected to vest		$ 6.36
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted Average Remaining Contractual Term		8 years 5 months 1 day		8 years 6 months 3 days
Weighted Average Remaining Contractual Term, Exercisable		7 years 8 months 12 days
Weighted Average Remaining Contractual Term, Vested and expected to vest		8 years 5 months 1 day
Weighted average grant date fair value		$ 22.46	$ 0.22
Intrinsic value, exercised | $		$ 400,000
Intrinsic value, outstanding | $		$ 45,100,000