Commitments and contingencies - Non-cancelable operating leases (Details)	12 Months Ended
	Dec. 31, 2020 USD ($)
Auburn Washington [Member]
Rent Expense [Line Items]
Rent expense	$ 60,000
Lease Expiration Period Description	Month to Month
Baton Rouge Louisiana [Member]
Rent Expense [Line Items]
Rent expense	$ 24,600
Lease Expiration Period Description	Month to Month
Champaign Illinois [Member]
Rent Expense [Line Items]
Rent expense	$ 654,000
Lease Expiration Date	Dec. 01, 2024
Champaign, Illinois (2nd location) [Member]
Rent Expense [Line Items]
Rent expense	$ 305,000
Lease Expiration Date	Sep. 01, 2021
CharlotteNorthCarolina [Member]
Rent Expense [Line Items]
Rent expense	$ 31,000
Lease Expiration Date	May 01, 2021
EscondidoCalifornia [Member]
Rent Expense [Line Items]
Rent expense	$ 219,000
Lease Expiration Date	Jun. 01, 2022
HampsteadNewHampshireMember [Member]
Rent Expense [Line Items]
Rent expense	$ 33,000
Lease Expiration Date	Aug. 01, 2022
Long Beach California [Member]
Rent Expense [Line Items]
Rent expense	$ 27,600
Lease Expiration Date	Feb. 01, 2022
Long Island City New York [Member]
Rent Expense [Line Items]
Rent expense	$ 815,000
Lease Expiration Date	Jul. 01, 2021
OntarioCaliforniaMember [Member]
Rent Expense [Line Items]
Rent expense	$ 110,400
Lease Expiration Date	Dec. 01, 2021
Pearl River New York [Member]
Rent Expense [Line Items]
Rent expense	$ 150,000
Lease Expiration Date	Dec. 01, 2021
RiversideCaliforniaMember [Member]
Rent Expense [Line Items]
Rent expense	$ 27,000
Lease Expiration Period Description	Month to Month
Rantoul, Illinois [Member]
Rent Expense [Line Items]
Rent expense	$ 36,000
Lease Expiration Date	Feb. 01, 2021
SmyrnaGeorgiaMember [Member]
Rent Expense [Line Items]
Rent expense	$ 465,000
Lease Expiration Date	Jul. 01, 2030
StonyPointNyMember [Member]
Rent Expense [Line Items]
Rent expense	$ 105,000
Lease Expiration Date	Jun. 01, 2021